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."
