I think keeping the #1 ranking will be difficult this year unless Nadal has another post Wimbledon slump, which I don't expect. Especially if Nadal does play one or two clay tournaments after Wimbledon. Nadal is getting closer, Federer can't afford to lose early in any of the TMS after Wimbledon
It's very sad that Roger lost so early from IW, Miami and Rome, and now to withdraw from Halle. When Nadal had his post Wimby 2006 slump that was after he'd already defended all his important titles and the clays season was over. Nadal was in no danger of losing his #2 spot with that slump.
Roger is having the adductor trouble going into his best tournament ... Wimbledon. This is not good. Let's hope Roger's confidence is not going to be low and that the draw is not going to give him some first or second round nightmare.