The Black Cats midfielder has been struggling with the injury for some time and visited a specialist earlier this week.
O'Neill said: "He went to see the specialist and he has given him an injection.
"At this moment, he is hoping in the next couple of weeks that that would cure things.
"But if it didn't do, then we might have to have another look at things, so we will see how it goes.
Asked if surgery was a possibility, O'Neill added: "That has been mentioned, but we will see.
"I wouldn't start to draw too many conclusions from that at the moment, but that might be the case."