Olympic pull-out was a hard decision: Nadal

Madrid: Rafa Nadal fears the chance to carry Spain's flag at an Olympics opening ceremony may not come around again after being forced to withdraw from the London 2012 tennis event with a knee injury.

The 11-times grand slam champion was to be his country's flagbearer at next Friday's opening ceremony but pulled out on Thursday after failing to recover from the knee problems that have dogged him.

The Olympic singles champion now faces a battle to be fit for the forthcoming U.S. hardcourt season culminating at the U.S. Open at Flushing Meadow.

Speaking to Reuters Television in a gym on his home island of Mallorca on Saturday, the 26-year-old said it had been a hard decision to withdraw.

"I was like scared to take the decision no? It is something that happens. You never know if it happens only one time in life bringing the flag of my country to the Olympics with all the sports family of Spain there," he said.

"All I can say is that I did as much as I could to be there and to be ready but it wasn't the right time.

"My emotion and my illusion [dream] to compete in the Olympics was more than ever.

"The only thing that I can do is to work hard and try to do the things that will create another opportunity in Rio 2016," added the former world number one.

"When I had to take the decision was the toughest moment. But it was something that I was thinking was going to happen for the last six, seven days because the knee was not improving."

Nadal suffers with tendinitis in his knees - a condition that forced him to withdraw from Wimbledon in 2009, a year after winning the tournament.

Only in March this year, he was forced to concede his Miami Masters semi-final against Andy Murray.

Despite winning a seventh French Open title, Nadal has dropped to three in the world rankings behind Roger Federer and Novak Djokovic and the state of his knees is sure to become a topic of debate as the American swing begins.

"The only thing I can do is to work hard every day as much as I can to try to recover my knee as quick as possible in the tennis calendar," said Nadal, who suffered a shock second-round defeat to Czech Lukas Rosol at Wimbledon last month.

"The tournaments never stop so I will try to be ready for the American season but you never know you have to work hard everyday and see, go day by day and see how it improves."

"I will compete when my knee says I am ready to compete," he added. "I don't want to go on court with bad feeling because then it is terrible. You start, you have to stop, you suffer every day. I will go back to court when my knee is ready."

Spanish basketball player Pau Gasol has been chosen to replace Nadal as the country's flag bearer.