MADRID, Spain — Defending champion Rafael Nadal pulled out of the London Olympics on Thursday with an undisclosed injury, leaving the tennis competition without one of its leading stars and robbing Spain's team of its flag-bearer for the opening ceremony.

Nadal won the French Open for a record seventh time this year but has struggled with left knee problems at times during the season. Shortly after winning his 11th Grand Slam title at Roland Garros, he lost to 100th-ranked Lukas Rosol in the second round at Wimbledon.

Nadal has not played since.

The third-ranked Nadal said Thursday he wasn't in condition to compete at the Olympic tennis tournament - which also will be held at Wimbledon.

"This is one of the saddest moments of my career, " Nadal said in a statement. "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.

"I tried to hurry my preparations and training to the very last minute, but it was not to be."

The 26-year-old Spaniard has won two Wimbledon titles and claimed gold at the 2008 Beijing Olympics.