O’Neill said: “When he came in here, he set the place on fire in his early games, which was a difficult standard to live up to. He knows he can play much, much better and much more consistently. I thought that he played well against Arsenal, but it was a pretty stodgy performance on Sunday.
“I just think that when he gets all these things clear in his mind, he’ll be fine – the change from Glasgow to Birmingham, the change of football. All of these things, he’s got to come to terms with. I think we’ll see a different Stiliyan Petrov next season. I would have expected him to have made a real consistently strong impact. I think he’s capable of doing that but it hasn’t shown. The West Ham game was extraordinary but those performances have been too few and far between. I thought his first-half performance at Sheffield United when he scored a goal was absolutely outstanding.
“That’s the sort of form he can achieve when fully confident but like a number of players here at this minute, confidence is a wee bit low. That stems from not winning the number of games that we would hope to have done. I suppose there are echoes of his start at Celtic. When I arrived at Celtic Football Club he was just trying to find form.
“He had been playing in a number of positions, so to find the right position for him obviously helped a great deal. But in fairness he was a lot younger then and you could understand it.
“Here he’s got more maturity about him and the move here should not have caused him the hassle that perhaps it has done.
“I think that after a few months players should settle down and be able to produce their best. Stiliyan has yet to do that consistently.”