Stamina is problem. He needs a rest for a couple of weeks to recharge so he can get back to the form he showed at the start, but Arsenal can't afford to with the horrendous run of games they've got. They should give him an hour each week then take him off so they can get a bit more quality but a bit less quantity.
Why Wenger didn't sub him I'll never know! Was never going to be his night after the penalty, and his confidence was in his boots - should have taken him out of the firing line at half time in my opinion