Hm, I don't think he's back in the thick of first team training at this point. A training report on Ajax.nl states "Zo moest Ajax nu nog steeds John O'Brien op het trainingsveld missen." which Babelfish translates to "Thus Ajax had now still John O'Brien on the training field missing."
Only thing that upset me about JOB is that after going to Amsterdam for a bachelor party last May and purchasing a replica at the Ajax store with his number on it, which was made in front of me (they had none already made), he goes and changes his number this year! Bah! Glad to hear he's staying at Ajax though.