The 27-year-old arrived at the Stadium of Light from Swansea in January as O'Neill invested £5million in an effort to take some of the burden off leading scorer Steven Fletcher.
However, in his six appearances to date, the last four of them starts, he is yet to add to his total of seven goals for the campaign at a time when the Black Cats desperately need firepower.
Time may not currently be on their side, but the manager remains confident that the two men will work well in partnership and that the newcomer will score goals.
O'Neill said: "He hasn't played that much for us. What Danny would have loved to have done is what Steven Fletcher did; come in, score goals immediately, win the fans over and play very well.
"At the moment, both he and the side are coming to terms with a change of pattern of play, but I have got no problems that he will get some goals for us.
"Obviously, he would like to get them as soon as possible. But during the course of time - he will take a little time to settle in, but sometimes it happens.
"Steven Fletcher got off to a flier and has kept it going. Danny hasn't been that lucky, but we will see. There's time."
Fletcher has contributed 11 of Sunderland's 33 league goals to date this season and with full-back Craig Gardner having added six more from his total of eight, the need for help is clear.
Graham forced an early save from Norwich goalkeeper Mark Bunn during Sunday's 1-1 draw at the Stadium of Light.
Indeed, it was his industry which sparked the 29th-minute incident that earned Bunn a red card.
However, neither he nor any of his team-mates was able to make Sunderland's advantage tell after Gardner had dragged them back into the game from the penalty spot.
The Black Cats have now gone seven league games without a victory and have taken only three points from the last 21 on offer, a return which leaves them just four points clear of the drop zone.
Graham is yet to taste victory in a red and white shirt and as long as his first goal eludes him, the frustration will grow.
O'Neill said: "He is one of those who definitely cares about not only the performance, but his participation in the team."