Nadal, the world's top-ranked tennis player, withdrew from the Queen's Club tournament, an important grass-court tuneup ahead of Wimbledon and which Nadal won last year. He cited knee problems for pulling out.
"I have been playing with pain on my knees for some months now and I simply can't go on like this," Nadal said in a posting on his Web site. "The pain was limiting certain movements in my body, which affected me mentally as well."
Nadal returned to Spain after his fourth-round loss May 31 at the French Open for medical examinations. Doctors determined he had "insertion tendonitis in the superior end of both kneecaps with a light osseous edema." They said treatment would include anti-inflammatory drugs and physiotherapy.
Nadal said he hoped to defend his Wimbledon title but added, "I will not go out and play, especially on the Wimbledon Center Court, if I am not 100 percent ready to play."