While I think a big factor in his performance tonight was fatigue (this was his 3rd match starting in 7 days), his form is really worrying. I don't think anyone expected him to be a Vidal-level midfield dynamo, but he's having trouble making simple passes and combining plays with his other midfielders and the left back. Even his first touch is often poor, which is compounded by the fact that he is easily muscled off the ball and can't win challenges. He wants to ping precision long-balls towards the forwards, but his inability to impose control on the midfield means they are either offside or it's easily cut out or intercepted.
Obviously with Marchisio next to him tidying things up he will look better, and I think he will sort it out once he gets more comfortable with our tactics and where his teammates are going to be, but so far he has been a huge liability in defense and has offered little in terms of ball control.