Rafael Nadal, who won men’s singles at the Beijing Games in 2008, withdrew from the coming Olympics in London on Thursday because of knee tendinitis, which was aggravated in his surprisingly early exit at Wimbledon.

The pageantry and magnitude of defending his gold medal and carrying the Spanish flag was not lost on Nadal, who called it “one of the saddest days of my career as one of my biggest ambitions, that of being Spain’s flag-bearer in the opening ceremony of the Games in London, cannot be.”

But “I do not find myself in a condition to compete,” he said, adding: “I have to think about my companions. I can’t be selfish, and I have to think of what’s best for Spanish sport, especially tennis and Spanish players, and give fellow sportsmen with better preparation the chance to compete.”

The London Games, of course, would have been a return to the All England Club, where Nadal, 25, won Wimbledon in 2008 and 2010.

Nadal is said to have hurt his right knee sitting in a chair before the Australian Open in January, but he reached the final there, losing a battle of endurance to Novak Djokovic.

Nadal did not play in February, choosing to rest his knees.

By mid-March, his left knee turned into a nuisance after a semifinals loss to Federer at the BNP Paribas Open. Later that month he withdrew just hours before the semifinal at the Sony Ericsson Open, blaming the knee.

“I saw that the situation was to be complicated to play,” Nadal said in March. “But, as always, I believe that things can improve. I did a lot of treatment, waiting. But I am not ready to compete. I am very sorry.”

For years Nadal’s knees have betrayed him — they prevented him from playing at Wimbledon in 2009; they forced him to retire in the quarterfinals of the 2010 Australian Open; and, perhaps, they have opened the door for Djokovic’s rise and Federer’s resurgence.

Then, last month at Wimbledon, Rosol, a 26-year-old journeyman, pumped winners, powered serves and pushed past Nadal, the world’s No. 3 player, who then withdrew from an exhibition scheduled against Djokovic a week later. Nadal’s aim had been to rest his knees. He tried to hurry his preparations and training, he said.

But on Federer’s grass, against Djokovic’s stamina, Nadal decided Thursday they would not stand up and “it was not to be,” he said.