HOUSTON -- Texans defensive end J.J. Watt is out for the season after he suffered a tibial plateau fracture in the team's 42-34 loss to the Kansas City Chiefs, coach Bill O'Brien said Monday. 
 
 Watt fell to the ground while engaged in a block on the Chiefs' opening drive. The veteran defensive end was helped to the sideline by the Texans training staff and was looked at in the sideline tent before being taken off on a cart. He was eventually taken to a hospital in an ambulance. 
 
 O'Brien also confirmed that outside linebacker Whitney Mercilus will be out for the remainder of the season with a torn pectoral muscle. 
 
 "The deal in this league is that the train doesn't stop moving," O'Brien said. "These guys are there, and they're going to have to step in. 
 
 "It's going to be multiple guys. You don't replace J.J. Watt or Whitney Mercilus with one guy. That's ridiculous. So it's going to a lot of different guys that are going to chip in to help." 
 
 On Monday morning, Watt tweeted to apologize to his teammates and the city of Houston. 
 
 I can't sugarcoat it, I am devastated. 
 
 All I want to do is be out there on that field for my teammates and this city. 
 
 I'm sorry. — JJ Watt (@JJWatt) October 9, 2017 
 
 Watt, 28, missed the last 13 games of the 2016 regular season because of a back injury. He played in his first regular-season game since his September 2016 back surgery in this season's opener against the Jacksonville Jaguars. In four games, Watt had 13 tackles, but he did not have a sack. ||||| Bob Levey/Getty Images 
 
 Houston Texans superstar defensive lineman J.J. Watt suffered a serious left leg injury Sunday against the Kansas City Chiefs in the first quarter and was unable to walk off the field under his own power. 
 
 The Texans announced Watt has a tibial plateau fracture, and head coach Bill O'Brien confirmed Monday that Watt will miss the season after Ian Rapoport of NFL Network reported the news Sunday night. 
 
 Watt was seen on crutches entering an ambulance after suffering the injury, per Aaron Wilson of the Houston Chronicle. 
 
 Watt and his brother T.J. tweeted about the injury: 
 
 Adding to the Texans' woes in Week 5, John McClain of the Houston Chronicle reported Whitney Mercilus needs surgery to repair a torn pectoral muscle suffered in the first quarter and will miss the rest of the season. 
 
 Injuries are becoming a worrying storyline for Watt. A back injury cost him all but three games in the 2016 season, and he dislocated a finger in the season opener, though he didn't miss a game. He also dealt with a broken hand in 2015. 
 
 When he's stayed healthy, he's been the most dominant defensive player in the NFL. In his first five seasons (2011-15), he registered 372 tackles, 74.5 sacks, 15 forced fumbles, 12 fumble recoveries and 45 pass deflections. 
 
 Pro Football Focus ranked him as its top player for the 2014 season and No. 5 player in 2015. He's a three-time Associated Press Defensive Player of the Year, four-time Pro Bowler and four-time first-team All-Pro selection. 
 
 Watt is the heartbeat of the Texans defense and recently used his platform to raise over $37 million in donations for relief for those affected by Hurricane Harvey as more than 200,000 people donated. 
 
 While the team managed to reach the postseason without Watt in 2016, the defense is far better when he's in the lineup alongside Jadeveon Clowney. 
 
 In his absence, Brandon Dunn, Joel Heath and Carlos Watkins should see more time in Houston's defensive line rotation. ||||| Joe Theismann put on his black trench coat and walked alone outside the suites at FedEx Field on Sunday afternoon, still upset by what he had just witnessed in Washington’s 23-21 loss to Houston. 
 
 “I still have goosebumps,” he said as he stuck his hands in his coat and made his way to the field. “I can’t believe it. November 18th is such a horrible day for Redskins quarterbacks.” 
 
 Earlier in the morning, the former Washington Redskins quarterback reminded his wife that it was the 33rd anniversary of the broken leg he suffered against the New York Giants on Nov. 18, 1985 – an injury considered one of the most gruesome in professional sports history. 
 
 Later in the day, he watched from a suite as current Redskins quarterback Alex Smith suffered a similar injury against the Texans, his right leg snapping in the same grisly fashion. Smith broke his right tibia and fibula, requiring immediate surgery, and he will miss the rest of the season, Coach Jay Gruden announced after the game. 
 
 Theismann said he became sick to his stomach as Smith lay on the turf, writhing in pain. 
 
 “I saw the way his foot was, and I turned away,” Theismann said. 
 
 [Redskins fall to Texans, 23-21, after Alex Smith is lost for the season with leg injury] 
 
 In the minutes after, as Smith’s leg was stabilized, and the quarterback was sent to the hospital and eventually diagnosed, Theismann sent out a tweet that compared his injury with Smith’s. He also texted Smith. He said he wrote to him: “I’m just so sorry.” 
 
 Alex’s leg is exactly like mine 33 yrs ago — Joe Theismann (@Theismann7) November 18, 2018 
 
 The memories of Theismann’s injury – which occurred after former Giants linebacker Lawrence Taylor barreled into the back of his right leg during a Monday Night Football game and effectively ended Theismann’s career – were even vivid before Sunday’s game. Theismann and his wife talked about the moment and the anniversary as they drove from Virginia to the game on Sunday. 
 
 He pointed out after the game that both he and Smith were at the late stages of their career when the injuries occurred. “You’re not 26, 27 years old. Alex is going to be what, 34 this year? I was hurt at the age of 35.” 
 
 There were other chilling ties to the two injuries : Both games ended 23-21 (although the Redskins won in 1985) and Texans defensive coordinator Romeo Crennel was on the sideline as the Giants’ special teams coach during Theismann game. 
 
 While Theismann was injured after being hit from behind, Smith’s occurred after his right leg had become caught in the turf during a sack by Houston defensive back Kareem Jackson. Texans defensive end J.J. Watt also made contact with Smith as he went down and his leg buckled. 
 
 Theismann launched a full-throated endorsement of Colt McCoy as the team’s starter moving forward, and he wondered aloud who the Redskins might turn to as the second quarterback. He also wondered, as he hurried down a stairwell and made his way out onto the concourse, when he might talk with Smith again. They now are bonded by a ghastly anniversary. 
 
 “I’m still just so upset,” Theismann said. “I feel so bad for him.” ||||| Photo: Karen Warren, Staff Photographer Image 1 of / 4 Caption Close Image 1 of 4 Texans defensive end J.J. Watt even beat the city's team owners in creating a fundraiser to aid in Houston's recovery efforts. The fund is up to $4,900,000. Texans defensive end J.J. Watt even beat the city's team owners in creating a fundraiser to aid in Houston's recovery efforts. The fund is up to $4,900,000. Photo: Karen Warren, Staff Photographer Image 2 of 4 Houston Texans defensive end J.J. Watt waves to the fans as he walks to practice during training camp at The Methodist Training Center on Monday, Aug. 21, 2017, in Houston. ( Brett Coomer / Houston Chronicle ) Houston Texans defensive end J.J. Watt waves to the fans as he walks to practice during training camp at The Methodist Training Center on Monday, Aug. 21, 2017, in Houston. ( Brett Coomer / Houston Chronicle ) Photo: Brett Coomer, Staff Image 3 of 4 Long a fan favorite, three-time NFL Defensive Player of the Year J.J. Watt, right, has continually been forced to raise his fundraising goal upward as people respond to his call for help. Long a fan favorite, three-time NFL Defensive Player of the Year J.J. Watt, right, has continually been forced to raise his fundraising goal upward as people respond to his call for help. Photo: Brett Coomer, Staff Image 4 of 4 Houston Chronicle columnist Brian Smith Wednesday, March 30, 2016. ( Karen Warren / Houston Chronicle ) Houston Chronicle columnist Brian Smith Wednesday, March 30, 2016. ( Karen Warren / Houston Chronicle ) Photo: Karen Warren, Staff J.J. Watt and his followers have your back, Houston 1 / 4 Back to Gallery 
 
 He has been a beacon during the devastation and chaos. 
 
 I'm not saying J.J. Watt has been a hero. That is a revered word reserved for the mostly anonymous, who have risked their lives over and over to save and preserve others, ever since Harvey wrecked Houston. 
 
 But true colors and real people shine through during times like this. And we've seen the best of this city's most famous athlete since a Category 4 hurricane became the flood that won't end. 
 
 A week ago, Watt was with the Texans in New Orleans, playfully asking his 3.9 million Twitter followers where the best place was for a beignet. He took a ride around the city. He played one series in a pointless preseason game against the Saints. 
 
 Then Friday, there was just this: "Stay safe Houston. We're thinking about you." 
 
 Translator To read this article in one of Houston's most-spoken languages, click on the button below. Brian T. Smith 
 
 Two days after that - on Sunday, when Harvey's local destruction was becoming a numbing reality - Watt posted the first of the personal videos that haven't ended. 
 
 He didn't wait for anyone else to speak up first. He beat Bob McNair, Leslie Alexander, Jim Crane and so many others to the podium. Watt composed an honest message, reached out to all those who follow him and shined a spotlight on Houston's unthinkable struggles. 
 
 "That's our city. It's very tough to watch your city get hit by such a bad storm and not be there to help. … So what I do want to do is, I want to start a fundraiser, because I know that these recovery efforts are going to be massive," Watt said. "There's going to be a whole bunch of people that we need to help get back on their feet and there's going to be a lot we need to do to help rebuild." 
 
 His goal was $200,000. 
 
 Watt brought it halfway himself, donating $100,000 to the Houston Flood Relief Fund for Hurricane Harvey victims at YouCaring.com/JJWatt. 
 
 The same day that No. 99 posted his first video - staring into a lens; simple and direct with no fancy production tricks - he was forced to add this: "Hey @youcaring I think we may have broken the website. Can you please help so that we can raise as much money as possible for these folks???" 
 
 And this: "The initial 200k was raised in less than 2 hours. I have now raised the goal to 500k. Your support is phenomenal!" 
 
 New Rockets guard Chris Paul soon kicked in $50,000, which allowed Watt to reach his second goal within 24 hours. 
 
 The videos just kept coming. As did a CNN appearance to promote the fund and raise more donations for Harvey victims. 
 
 "$1 MILLION! New Goal: $1.5 Million," Watt tweeted. 
 
 "$2 MILLION! New Goal: $3 Million," just 16 hours later. 
 
 As I type this, the current total is more than $4,900,000 which has been raised by 48,565 donors in only two-plus days. 
 
 Remember when hating on the three-time NFL Defensive Player of the Year was so hip and cool? 
 
 Too many commercials. Too much endless attention. Total overexposure. 
 
 Uhhh, hey J.J. … Houston will never forget this. 
 
 "It's been an unbelievable display of what can happen when people come together. … That's what Houston's all about," Watt said. "It's a very diverse city. It's a very resilient city. It's been through things like this before - maybe not of this magnitude, but it's been through these types of situations. People are coming together, people are helping raise each other up." 
 
 Bill O'Brien gave a shoutout to Watt's efforts while the Texans adjusted to their temporary home in Frisco. The team's coach then issued his strongest statement since he became a Houstonian, again proving that he runs much deeper than his tough exterior. 
 
 "We're going to dedicate this season to the city of Houston, the people of Houston," an emotional O'Brien said. "There are no guarantees in football. … But I will guarantee that this team will go out every Sunday, Monday, Thursday - whenever they ask us to play - and we'll play our (butts) off for the city of Houston. I promise you that." 
 
 Since Watt started his fund, McNair's Texans pledged $1 million to the United Way, which was matched by the NFL Foundation. Crane's Astros have promised $4 million that will go toward Harvey relief efforts. 
 
 Alexander one-upped them all, increasing his initial $4 million pledge to $10 million Tuesday. 
 
 The same day, Tennessee Titans owner Amy Adams Strunk donated $1 million to the fund that Watt started with one short video. 
 
 "Humanity is incredible. The positive vibes are unbelievable," Watt said. "Houston, we're all thinking of you. The whole world is wishing you the best. Stay strong. We've all got your back." 
 
 The money will obviously have to be followed. But Watt long ago proved his foundation's worth when it comes to charity, and he has touched the lives of everyone from firefighters and teachers to young athletes and sick children. 
 
 "I'm working very hard … to make sure this money goes directly to the people, not to administrative fees or anything like that," Watt said. 
 
 To the people. 
 
 On the playing field, Watt's at his best surrounded by adoring thousands. Because of Harvey, many who love him are now just trying to hold on and survive. 
 
 During some of the darkest days in this city's history, it has been impossible to doubt the power and sincerity of No. 99.
– Houston Texans fans who have been holding their breath since their superstar defensive end JJ Watt went down with an injury in the first quarter of the team's 42-34 loss to the Kansas City Chiefs Sunday had their collective hearts broken on Monday, per Bleacher Report. After the Texans tweeted Sunday evening that Watt, a three-time NFL Defensive Player of the Year, had suffered a tibial plateau fracture in his left leg, head coach Bill O'Brien confirmed that the injury had ended Watt's season. Early Monday morning Watt tweeted, "I can't sugarcoat it, I am devastated. All I want to do is be out there on that field for my teammates and this city. I'm sorry." Watt's injury occurred at the seven-minute mark of the first quarter. While attempting to work his way around the Chiefs' offensive line he appeared to have his leg run into by his own teammate, causing him to fall to the ground. Watt was escorted to the sideline by Texans staff and eventually put into an ambulance and taken to a hospital, ESPN reports. Making matters worse for the Texans, Watts' teammate Whitney Mercilus was also forced to leave Sunday's game with a season-ending injury. Watt, 28, sat out most of last season with a back injury.