O’Neill 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.
"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."
After seeing Sunderland take seven points from their six Premier League fixtures so far, O'Neill added: "We've made a solid start to the season and I'm not unhappy with it.
"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."