He had a back injury, and was also nursing a hand injury he got during the off-season. He also seemed like he didn't care that much, he was going very quickly between points he wasn't even bouncing the ball anymore. IF you have watched him before he bounces the ball a lot. He should have just skipped the Australian Open and gave it to someone that is fit enough to play. He was contemplating on not playing in the AO.
Waste of a trip then! What's the point of going if the heart's not in it?