Those watching today's practice session were not very encouraging - tweeted that there were lots of stops, lots of back clutching and balls missed all over the court - doesn't sound great.
I just hope he hasn't messed up his back again. He did hold it at one point in the 3rd against Nalbandian after stretching for a ball, and the comms noticed it too. If he has, then prepare for a withdrawal. On the other hand he could just be stiff after that match, given it was his first for over two weeks.