O'Neill said: "From where we stand, there has been a remarkable change because he does look very calm.
"Since I don't really know him, and I'm making a judgment from outside, this appears to be the way he has chosen to manage. He has chosen not to be growling from the sidelines. From the outside it looks like a change and, so far, it's worked for him."
O'Neill always wears a tracksuit and paces the dugout area during matches. His water bottles take a particular pounding.
He admitted: "I don't know if I'd ever change. People say 'go on and wear a suit.' Graeme Souness offered me that advice when I was at Leicester but I chose not to.