Graham was bought from Swansea City for £5m two months ago but has yet to find the net as a Black Cats player.
O'Neill told reporters: "We said before that we have relied very heavily this season on Steven Fletcher scoring the goals, more so than we should have done.
"We needed some sort of experienced player in there alongside him.
"I thought Danny fitted the bill and I do believe that he will get goals when he gets fully match fit. He'll prove a handful."
Sunderland face off against Norwich City on Sunday.