Gordon arrived at the Stadium of Light after completing a £9 million move from Hearts, which was the British transfer record for a keeper in 2007.
The 29-year-old had a fantastic first season and his reputation continued to rise. However, a series of serious knee injuries has meant he has been unable to feature on a regular basis over the last year.
The Scottish international’s contract is set to expire this summer which would allow him to leave Sunderland on a free transfer. But O’Neill is positive his current third-choice shot-stopper can put his injury demons behind him and get his Sunderland career back on track.
The former Aston Villa boss told The People: “I have spoken to Craig and he has to get himself absolutely fit.
“If he is fit and properly raring to go at the end of the season, and is reaching anything like the form of previous times, he will be in demand, from both ourselves and other clubs.
"Once Craig is absolutely pain-free, then I think that's the time to make a judgement."
The ex-Hearts man has only played one reserve game in recent weeks, but has been named in Craig Levein’s Scotland squad for the international friendly in Slovenia.
O’Neill added: “I'm not sure whether Craig would be the No.2 or what, but it is great for his confidence and it is a big boost for him."