Madrid: World number one Rafa Nadal has enjoyed one of the most successful seasons in tennis but the Spaniard thinks winning the four Grand Slams in a single season is beyond him.
Nadal, top seed at the Shanghai Masters, has won Wimbledon and the US and French Opens this season, plus a string of Masters and other titles over a blistering 10 months.
However, he was forced out of the Australian Open quarter-finals in January due to a knee injury.
"For me, winning the four titles is impossible," said the 24-year-old on Tuesday ahead of his first round match at the Shanghai`s Masters.
"I will try to keep playing well and to try to win four titles next year. But it may not be case they are all Grand Slams. That`s impossible for sure, I think," he added.
Nadal, who has already secured the yearend number one ranking with several tournaments to spare, admitted to fatigue due to a hectic 2010 tour schedule.
"I am a little bit more tired than usual. But this is because I have probably played more matches than the rest," he said.
Nadal, who was re-elected a member of the Tennis Player`s Council, said there was a growing belief that changes had to be made to help the next generation of players.
He added that there should be a shake-up of the system in order to allow a longer close season without putting ranking points at risk.
"The perfect schedule is if you have the chance to play and you have the chance not to play," he said.
"My feeling always has been -- and everybody knows this because I say it at the council a lot -- that after the US Open, you can play here in Asia for two weeks or three weeks maximum," he said. "You play the Masters and that`s it for the season."
Players currently only get a month`s rest from the grueling Tour circuit, and some claim this can lead to injury or burnout.
The left-hander said a compromise had to be reached to allow lower-ranked players the chance to earn as much as they could, without denying top players points and rest.
One answer could be the option of stopping playing after the high-scoring Masters calendar and not being obliged to play in the low-scoring international tournaments, he suggested.
"Novak Djokovic, probably Roger Federer, me and other guys on the council are working for the next generation, not for us," he said.
Any changes would probably come too late to make an impact on his own career, he added.
"But if things can be better for the next generation, I will be happy for that," he said.