WIMBLEDON, England - Rafael Nadal figured he couldn't win Wimbledon this year because of his achy knees, so he decided it didn't make sense to try.

Nadal withdrew from the grass-court Grand Slam tournament yesterday, three days before it begins, becoming only the second men's champion in 35 years to decline to defend his Wimbledon title.

"When I start a tournament like Wimbledon, it is to try to win," the No. 1-ranked Nadal said, "and my feeling right now is I'm not ready to play to win."

A subdued Nadal, wearing a purple T-shirt and white pants, spoke at a news conference yesterday at the All England Club, in the same room where he took questions after beating Roger Federer in the epic 2008 final that ended after 9 p.m. with light fading.

The 23-year-old announced his withdrawal about 21/2 hours after losing to 18th-ranked Stanislas Wawrinka in an exhibition match on grass at the Hurlingham Club in south London.

"Today was the last test. I didn't feel terrible, but not close to my best," said Nadal, who also lost an exhibition match against 2002 Wimbledon champion Lleyton Hewitt on Thursday. "I'm just not 100 percent. I'm better than I was a couple of weeks ago, but I just don't feel ready."

Nadal called it "one of the toughest decisions of my career," but he added: "There's no option. I don't feel ready to compete 100 percent for two weeks."

He is the first reigning Wimbledon men's champion to pull out of the following year's tournament since Goran Ivanisevic in 2002. Otherwise, it hadn't happened since 1973, when Stan Smith opted not to defend his Wimbledon title because of an ATP boycott of the tournament.

Nadal has complained about his knees since a fourth-round loss to Robin Soderling in the French Open on May 31 ended his streak of four consecutive championships at Roland Garros. Later that week, Nadal pulled out of the Wimbledon tune-up tournament at the Queen's Club, then went to Barcelona to have tests on his knees.

"I think I reached the limit right now. I need to reset to come back stronger," Nadal said.

Asked what sort of threat the knee problems might present to his career moving forward, he said: "It's not chronic. I can recover, for sure."

His exit opens the door for Federer to reclaim the No. 1 ranking, a spot he held for a record 237 consecutive weeks until Nadal pushed him down to No. 2 in August. Federer, who is 7-13 against Nadal, also avoided facing him in the French Open. Instead of a fourth consecutive final in Paris against Nadal, Federer faced Soderling for the championship June 7 and won in straight sets to complete a career Grand Slam and tie Pete Sampras' record of 14 major titles.

Aside from the physical issues, Nadal spoke yesterday about the mental toll the injury has taken. This is, after all, a player whose rise to the upper echelon of tennis was built in part on his ability to race around a court and track down shots.

"One of the big problems is, when I am playing, I'm thinking more about the knees than about the game. So that's very difficult to play well like this, no?" the six-time major champion said.

By pulling out after yesterday morning's draw, Nadal forced organizers to shuffle the men's bracket. No. 5-seeded Juan Martin del Potro was moved from a potential semifinal against No. 2 Federer on the bottom half of the field into Nadal's old spot in the top half. And No. 17 James Blake switched from the top half to the bottom half in del Potro's old spot - and a possible semifinal against Federer.