The 19-year-old arrived at the Stadium of Light in an £8.1million switch from Ipswich during the summer of last year with a big reputation.
However, chances had been few and far between under Steve Bruce, the man who signed him, and successor O'Neill - 14 of his 19 appearances last season came from the bench - until Steven Fletcher's injury problems handed him a chance to show what he can do.
The Ulsterman started Wickham in his first two games as Sunderland manager, but has since used him sparingly.
However, he has been impressed with what he has seen on and off the pitch in recent weeks and is demanding more of the same.
He said: ''I am seeing an improved player. He's doing a lot of work. He has started to realise what a professional footballer is all about, and he wants to try to do things properly.
''I'm not saying he wasn't before that in that sense, but I think he is starting to realise what the game is about.
''The sort of position he plays within the team is very, very important, and he has got to show those attributes.
''Physically, he is very strong and he has got to show those attributes that I think he possesses.''
Wickham's latest opportunities have comes as a result of leading scorer Fletcher's misfortune with first an ankle injury and more recently, a back problem having limited the Scotland international's participation.
The youngster started the 3-1 home defeat by Chelsea on December 8, his only senior 90-minute appearance of the campaign to date, and is on stand-by for tomorrow's trip to Saints with seven-goal Fletcher facing a late fitness test after hurting his back at Manchester United last Saturday.
Full-back Danny Rose missed that game with an ankle problem and he too faces a race against time to prove his fitness.
Rose's form has been one of the bright spots in a difficult start to the season for the Black Cats, and O'Neill has made no secret of the fact that he would like to add his to his squad on a permanent basis.
However, Tottenham have the right to recall the defender, as they are entitled to do under the terms of his loan agreement, next month, while there has been speculation that another club could launch a transfer bid with QPR having been linked with him this week.
O'Neill, however, remains relaxed, confident not only that Spurs are content to leave the player where he is, but that Rose himself is happy to stay.
Asked if he feared his hand might be forced to make a move in January, he said: ''No, I am not at all.
''Danny has improved here at Sunderland and he is enjoying it immensely.
''Spurs are getting their players back from injury. At this minute, of course they have the ability to recall him and there's nothing you can do about that.
''But as for the rest of it, no, he is enjoying it immensely here and I think we have been good for him.
''I'm not so sure your hand would be forced in January in that sense.''
O'Neill confirmed he will recall Republic of Ireland midfielder David Meyler from his loan spell at Hull after tonight's Championship trip to Derby with difficult home clashes with Manchester City and Tottenham to come over Christmas and skipper Lee Cattermole sidelined by a knee injury.
Given what lies ahead, a win over the Saints would provide a significant boost, although the 60-year-old knows that will be easier said than done.
He said: ''They are playing well. They seem to have overcome their initial difficulties in the league, they are getting used to it now.
''Like ourselves, they retain a good spirit and they are in decent form themselves.''