Originally Posted by DyronNix
Nadal hasn't had any knee surgery. He has undergone some pretty aggressive knee therapy including as I understand it some form of blood/stem cell transfusions into his knees that helped tremendously a few years ago.
Hard courts aren't his best surface by far, but he is no slouch on them either. He's won the AO once and should've won last year (up a break in the 5th).
There are only so many slam opportunities in one's career. I know Rafa doesn't take them lightly and that is why I am concerned that he may be more injured than he's telling the public.
I think he probably believes that if he starts off on clay courts that he can go into Wimbledon with fresh knees, and then -- as grass isn't particularly hard on the knees either -- make another run at the US Open.
The Aussie hard courts are slower than the US Open hard courts, which is why he has had more success at the Aussie than at the US Open. But I think he basically didn't believe that he was in good enough form to have a chance of winning the Aussie, so he pulled out to save his knees for the clay court season.