Australian Open: QF. 4RD exit or earlier is possible, he's rusty and never plays well here
Wimbledon: 4RD/QF. SF/F if things go his way with the draw. he is still a better grass court player than djokovic and murray, though murray is catching up.
Us Open: QF, early exit possible. shouldn't put too much focus on this, he has one already, the one he needed for the collection
We don't know whether he can return playing at the same level, but if he does, these predictions are very pessimistic (assuming you want the best for him).
AO: last 4 results (W, QF, QF, F). Seems more reasonable to suggest he is huge favourite to reach at least the SF if he is fit.
Wimbledon: Last 4 results (W, W, F, 2R). Not sure what to make of the Rosol match but assuming no more freak results, Nadal should be favourite against everyone but Djokovic here in latter stages (always favourite vs Federer now, 3-0 record vs Murray, 1-0 record vs JMDP).
US Open: Last 4 results (SF, SF, W, F). Predicting anything less than a SF here is inexplicable considering his recent record.
It's easy to predict Nadal to lose early when far away from an event, but people forget how difficult it actually is to do. Nadal is 57-2 against the rest of the tour (not Djokovic) since AO '10. That includes wins against Federer, Murray, JMDP, Berdych, Ferrer (one defeat to him also). So, realistically, betting against him in a grand slam if his opponent isn't Djokovic makes little sense unless this injury has permanently effected him. Many people seem to be talking as if Nadal has declined seriously, but his results in grand slams have never been more consistent. There are only two differences between 2010 and 2011-2012, one is Novak Djokovic, the other is the freak performance by Rosol. As for Novak, that's a problem for Nadal, but shouldn't be a reason to start predicting 4R and QF defeats. As for Rosol, it can be interpreted many ways, but to imo, it really was just a freak performance, out of Nadal's hands. He has played worse than that to win early rounds in Wimbledon before, just got unfortunate with an on fire opponent.