Rafael 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 US hardcourt season culminating at the US Open at Flushing Meadow. Speaking to emReuters Television /emin 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. [caption id=attachment_386432 align=alignleft width=380