O'Neill is well aware of the galvanising effect the former Tottenham manager's arrival could have on an expensively-assembled squad.
He said: "We are not capable of treating anybody lightly, far from it. We are not good enough to do that at all.
"But in many aspects with him coming in, it's a game for us that we know now the players' concentration has to be absolutely at its height.
"We have just got to go and try to create some chances against a side that looked as if it had played very well against Manchester United, so they will come, even though they haven't won yet, with plenty of confidence themselves.
"From all accounts - and I have watched a good deal of the game against Manchester United at Old Trafford - they played very well, took the lead and played very well up until the equalising goal.
"Manchester United, of course, are a very fine side, but in terms of performance, they will have gained a great deal from that."