Poor guy. Now his doubts about leaving will just increase exponentially. Not saying going to Bayern caused this injury, that would be absurd, however this is how the mind works.
He probably was hesitant and unsure about leaving Barca, he left because he wanted to play more. If he would have gotten a more playing time guarantee in Barca, I've no doubts he would have stayed. So now you couple the indecision of leaving with the fact that he hasn't triumphed immediately in Bayern and now the injury, the mind works in strange ways.