I don't think ir really about the wrist injury at this point. More the point seems to be he's not putting in the the off court work to be in top shape. The tired thing etc is not his wrist, it's he's not in good shape and hasn't been doing the work.
He always looks tired (a bit like Isner), doesn't necessarily mean he is. His fitness is only relatively poor compared to the other players ie Nadal, Djokovic, Federer, as expected really because those guys are fitness machines. He's actually one of the few guys with better results in best of 5 than best of 3, the 5-set format isn't an issue, it actually makes him even less prone to upsets.
I think he is in good shape, his preparations for the USO were just hampered by his wrist injury so he has to play himself into form. His (relative) struggles against Serra and Harrison had nothing to do with fitness, just with some rustiness in his game.