Sunderland boss has joined the growing chorus backing the young Derry born star's chances of playing at the European Championship
The Sunderland boss, who handed McClean his debut for the Black Cats last December, was keen though not to pressure on Ireland's current manager to select his young charge ahead of Monday's squad announcement reports the Irish Times.
“I am not saying to put him into the team – I am not saying anything, really, because Trapattoni doesn’t need me to pick his team, he is doing that pretty well himself," said O'Neill.
He added: “But for James, it would be a fantastic experience, for a start. I actually believe he could make a contribution, even if it was coming off the bench.
“I would say that anyway, but he’s been terrific for us, really terrific, and he would certainly not be out of place, far from it. In fact, he could make a mark in that competition. But if he is not chosen for it, myself I wouldn’t be too down-hearted about it."
McClean has been in superb form for O'Neill since the Ulsterman handed him his Premier League debut late last year against Blackburn Rovers. He is expected to pick up the club's award for best young player after a stellar 2012.
"He hasn’t allowed his performances to drop too much since then (his debut). In fact, I think he has surpassed expectations. It’s been three-and-a-half months of just excellence from him, and naturally I’m delighted. He may well have surprised himself, really, by his consistency," said the Sunderland manager.
McClean's chances of making the Il Trap's final 23-man squad were given a boost after the Italian tactician said he had a '90 to 99 per cent' chance of being included.
The Republic of Ireland squad will be announced at 1530 Irish time on Monday.