Defending Olympic champion Rafael Nadal has pulled out of London 2012, saying he is "not in condition" to compete.
The 26-year-old is suffering from tendinitis of the knee and will be unable to defend the singles title he won in Beijing in 2008.
"I do not find myself in a condition to compete," he said.
"It is one of the saddest moments of my career."
The Spanish 11-time Grand Slam winner was expected to carry his nation's flag during the opening ceremony in London.
Nadal, ranked third in the world, became the first top-five male to win the Olympic singles when he beat Chile's Fernando Gonzalez in the final four years ago.
"I am not able to compete at the Olympics in London and therefore will not be traveling as planned with the Spanish delegation," he said in a statement on the Spanish federation (RFET) website.
"I have to think about my colleagues.
I cannot be selfish and I have to think of the good of Spanish sport, especially Spanish tennis, and let a team-mate who is better prepared to compete.
"I've waited until the final moment of my preparation and my training, but I cannot do it."
Nadal has a history of knee problems, with tendinitis ruling him out for much of the 2009 season and more recently forcing him to withdraw from a charity match against Novak Djokovic.
The two-time Wimbledon champion has not competed since his second-round exit at the All England Club in June, where he lost to then-world number 100 Lukas Rosol in five sets.
He will be hoping the prolonged break will increase his chances of being fit for the US Open, which begins on 27 August.