Madrid, July 29 (DPA) Rafael Nadal admitted that he faces a 'sea of doubt' about his chances of a successful return to tennis in August after missing two months with knee pain.

'I'm in a sea of doubt,' said the world number two, who lost his top ranking after crashing out of the French Open in the fourth round and then sitting out with knee tendinitis during Wimbledon, which was won by Roger Federer.

In his interview to Spanish television TVE, the four-time Roland Garros champion said his 'dream' is to return to the ATP for the Aug 9 start of the Montreal Masters after last playing a match on May 31, when he went out in Paris to Robin Soderling: 'I have to force the knees and just see how far I can go.'

Nadal had felt pain from the start of the European clay season and willed himself to play - and win - Monte Carlo, Barcelona and Rome over three consecutive weeks in April and May. 'I didn't know when to stop,' he said.

He said that playing in Madrid, where he lost the final to Federer after a marathon semi-final win over Novak Djokovic, was a step too far for his body.