Dale Earnhardt Jr. Is Sidelined by Concussions CONCORD, N.C. - Two concussions in a six-week span have forced Dale Earnhardt Jr. out of the No. 88 Chevrolet for at least two weeks in the middle of the Sprint Cup playoff race and raised questions about head injuries in the sport. Earnhardt revealed Thursday that he had sustained a concussion in an accident during a tire test at Kansas Speedway on Aug. 29 and continued to race. The ailment was not diagnosed until Wednesday, three days after he was involved in a multicar crash at Talladega Superspeedway that gave him a second concussion and led him to seek medical help. Earnhardt was examined by Dr. Jerry Petty, a neurosurgeon and consultant to Nascar and the Carolina Panthers of the N.F.L. Petty would not clear Earnhardt to get back into the racecar for practice at Charlotte Motor Speedway on Thursday in advance of Saturday's Bank of America 500, the fifth of 10 races in the Chase. Instead, Earnhardt will miss at least two races, including next week's event at Kansas. That will cost Earnhardt, who was 11th in the standings, any chance of coming back to challenge for the title this year. "For whatever the reason, the wreck at Kansas was just really severe and really surprised me how tough it was to get past that," Earnhardt said Thursday. I thought I was in the clear, but just that little accident at Talladega, I started having headaches and stuff immediately after the wreck, and then into the next day and into Tuesday, and I thought, man, this is pretty soon after the other accident in Kansas. I should probably take this really seriously and seek some professional opinions on this. At Talladega, Earnhardt was caught in the middle of a 25-car crash on the final turn of the Cup race. He will now have to wait until after his headaches subside before he can tested and cleared to race. The former driver Ricky Craven, who missed time in 1997 and "98 after sustaining a concussion in a wreck, said Earnhardt could be out much longer. "If it's serious enough to lose two weeks, then I automatically start thinking, then maybe it's serious enough to lose six weeks," said Craven, now a broadcaster. Earnhardt will be replaced by Regan Smith of Cato, N.Y., who had been scheduled to race in the No. That ride instead went to A J Allmendinger, who lost his job at Penske Racing after failing a drug test but has been cleared to race again. Despite the concussions, Earnhardt did not criticize Nascar safety equipment, pointing to improvements in racecars and tracks made the last 10 to 12 years. Many of those changes came after his father, Dale Earnhardt, was killed in a crash on the final lap of the 2001 Daytona 500. Steve O'Donnell, Nascar senior vice president for racing operations, said drivers had reported just nine concussions in the last five years. Most recently, a Nationwide Series driver, Eric McClure, sustained a concussion at Talladega in June after a hard hit on the inside wall. He missed five races before being cleared to compete again. Given the number of crashes from week to week, O'Donnell believes the few reported concussions are proof the sport is safe. But what of drivers who have concussions that aren't reported? "I'm sure drivers have and didn't even know they have," said the defending Cup champion, Tony Stewart, whose attempted block at the front of the pack caused the wreck at Talladega. That's the thing. It's not different than football or any other sport where you get bounced around. I'm sure there's been a lot more than knew they had it. Of course, the potential for danger is greater in Nascar if a driver with a head injury is on the track at 200 miles an hour. But missing even one race can be devastating to a driver's chances of winning a championship or even keeping a ride, which is why there is some question if drivers would hide symptoms of a concussion. Earnhardt was lauded for seeking medical help, giving up any chance to go for the title. The driver Jeff Gordon said he would not go to a doctor to be checked for a concussion if it might cost a chance at a championship. "No, I wouldn't," he said. That's the competitor in me and probably many other guys. And that's to a fault. That's not the way it should be. I think that's what gets a lot of us in trouble.