Champion Rafael Nadal is a doubt for this year's Wimbledon championships because of a knee injury, his coach said. "We will see on Monday or Tuesday. We will go to Barcelona to see what the problem is. I am not too optimistic," the world number one's uncle and coach Toni Nadal told a French radio.

"Of course, if there is a possibility for him to take part in one the world's greatest tournaments, he will. "He is very affected by this."

The Spaniard had already pulled out of next week's warm-up tournament at Queen's Club and now faces the possibility of missing the season's third grand slam, which begins on June 22. Nadal's four-year reign at the French Open was ended by Swede Robin Soderling in the fourth round. He also lost to Roger Federer in the Madrid Open final last month.

Although the world number one did not complain of any knee problems following those defeats he has been plagued by tendinitis in recent years. A gruelling claycourt season, during which he won titles in Monte Carlo, Rome and Barcelona, appears to have taken its toll on the 23-year-old.