Golf No.1 McIlroy walks off the course as form slump continues Rory McIlroy and his caddie J.P Fitzgerald walk off the course after the Northern Irish stars pulls out of the second round of the Honda Classic. Rory McIlroy walks off the course during disastrous second round in Florida No.1 cites a troublesome wisdom tooth for his sudden withdrawal Honda Classic title holder McIlroy was seven over par after eight holes at PGA National He has suffered a form slump since a big money switch to Nike (CNN) -- In a season of lows, golf's No.1 Rory McIlroy hit a new low as he simply walked off the course following a disastrous start to the second round of his defense of the Honda Classic title in Florida. McIlroy was seven over par for eight holes and about to drop more shots after hitting his approach to the 18th -- his ninth -- into the water at PGA National. The Northern Irishman shook hands with his playing partners Mark Wilson and South Africa's Ernie Els and beat a hasty retreat with his coach and his caddie. Golf journalist David Dusek, tweeted that McIlroy "was near tears as his caddie placed his clubs into the trunk of his blue BMW." McIlroy later issued a statement apologizing for his "sudden withdrawal." He added: "I have been suffering with a sore wisdom tooth, which is due to come out in the near future. It began bothering me again last night It was very painful again this morning, and I was simply unable to concentrate. It was really bothering me and had begun to affect my playing partners. I came here with every intention of defending my Honda Classic title. Even though my results haven't revealed it, I really felt like I was rounding a corner. I regret having to make the decision to withdraw, but it was one I had to make. McIlroy had battled to a level par first round at Palm Beach Gardens -- six shots behind first round leader Camilo Villegas of Colombia -- but had to rely on his recovery play around the greens to preserve his score and he finished with a bogey six on the 18th. Read: McIlroy and Woods trail in Florida But he was in good spirits Thursday night in a family occasion, tweeting: "Having a great dinner celebrating my mums birthday!" That optimistic mood would have been quickly shattered by his performance on the course Friday morning. Starting at the 10th hole, McIlroy was quickly in trouble, hitting his approach to the 11th into the water and running up a double bogey. A further bogey followed on the 13th before a disastrous display on the 16th where he found the water twice and ran up a triple bogey seven. Three putts from 40 feet on the par-three 17th left him seven over for the tournament and with little chance of making the halfway cut before he found yet more water on the testing par-five finishing hole. It is the first time the 23-year-old McIlroy has pulled out of a tournament. McIlroy's stumbling start to 2013 is in sharp contrast to his dominant displays last year and comes in the wake of signing a lucrative 10-year sponsorship deal with Nike, worth a reported $250 million. Honda Classic: Latest scores As part of the deal, McIlroy changed his golf clubs to play with Nike branded equipment, which is also endorsed by his great rival and World No.2 Tiger Woods. He has enjoyed his previous success, including two major victories, playing with rival Titleist clubs. Results since have not lived up to expectations and he missed the cut in Abu Dhabi in his first tournament of the year. That was followed by a sorry first round exit -- Woods also went out on the same day -- at the WGC Accenture World Matchplay event in Arizona last week. Critics have also focused on the scale of McIlroy's new commercial ventures and three days before his Honda Classic defense he signed a three-year deal with audio products and headphone manufacturers Bose. On the eve of the tournament, McIlroy took to Twitter again: "Had a great time with the Bose crew at the launch of our exciting new partnership last night. Looking forward to a great relationship. McIlroy, who dates former World No.1 tennis player Caroline Wozniacki, will get an early chance to silence the doubters as he is due to tee off next week in the WGC-Cadillac Championship on Doral's daunting Blue Monster Course. It is all part of his preparation for a tilt at the U.S. Masters in Augusta, one of his major targets for the year as he bids to build on a 2012 season when he topped the money lists on the PGA and European Tours and claimed the U.S. PGA Championship in stunning fashion.