He hasn't won a tournament on any surface other than clay in more than a year and a half.
So can 2010 U.S. Open champion Rafael Nadal be considered a serious contender for this year's Open?
The last time Rafa won a hard-court title was at Tokyo in October 2010, a month after defeating Novak Djokovic in the final to win his only U.S. Open at Flushing Meadow.
Injuries, fatigue and the form of Djokovic have combined to make the "King of Clay" vulnerable on anything other than his favorite surface.
Rafa's form leading into this year's clay-court season was patchy.
Despite taking six weeks off after losing to Djokovic in the Australian Open final, he failed to impress in the spring U..S hard-court Masters events.
Leaving aside the blue clay in Madrid, Nadal then won clay titles at Monte Carlo, Barcelona and Rome without losing a single set.
And at Roland Garros, Rafa won a record seventh French Open, losing just one set—to Djokovic in the final.
Rafael Nadal is unquestionably the greatest clay court player of all time.
But at Wimbledon Nadal suffered a shocking second-round defeat to world No. 100 Lukas Rosol.
And a recurrence of tendonitis in his knees led to the withdrawal of the defending gold medalist from the London Olympics.
It remains to be seen if Rafa will have recovered well enough for him to pose a serious threat in the U.S. Open lead-up Masters events at Toronto and Cincinnati.
Certainly Federer, Djokovic and Murray will be doing everything in their power to make sure he doesn't.
Personally I think it's unlikely Nadal will another tournament this year.
He may require a lengthy rest after the U.S. hard-court season, which is the most physically demanding surface to play on, particularly for someone struggling with bad knees.
It's not unusual for tennis players to take extended periods of time off the tour to rest, do rehab or, in exceptional cases, undergo surgery.
However, I wouldn't bet against Rafa coming back and being crowned 2013 Australian Open champion.
What do you think?