The Black Cats manager expects that his summer signing will need time to settle into the side after a spell on the sidelines and wants supporters to lower expectations for now
The England international signed from Manchester City in August for a fee in the region of £10 million but has largely been outshone so far by fellow recent acquisition Steven Fletcher.
But O'Neill feels that it is unfair to expect much of the 25-year-old, considering his recent injury problems and only being at the club for two months.
He told The Sunderland Echo: "I'm just a little concerned that people might be expecting him to come in and be winning every game for us because that's certainly not going to be the case.
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"He's a real talent, and I know he's going to be a great asset to this club. But he's only one player and it's a team game.
"Creatively, we have to be better and he has a part to play in that, but then so do other players.
"It's about everyone taking responsibility and working hard to make things happen."
The Black Cats boss is pleased with the start that his side have made to their Premier League campaign but concedes that he would like to see an improvement in their attacking play after the international break.
"We've made a solid start to the season and I'm not unhappy with it," O'Neill continued.
"Defensively we've been solid but we need to be more effective in the final third and that's what we're all working on.
"It's still the start of the season though and I know the squad will continue to improve as it progresses."