The 29-year-old, signed in a record £9million deal by Roy Keane from Hearts five years ago, is out of contract at the end of next month and looks certain to quit Sunderland after falling behind Simon Mignolet in the pecking order.
O'Neill said: "Ideally I would love to give Craig a game. His contract runs out at the end of the season and he can either be in a great position or wondering what will happen to him if he hasn't played. He has been out for a long, long time and it's getting back into the side to prove his point. That's been the difficulty.
"If our wage bill could allow it, I wouldn't mind having the three, but I'm not so sure that players of that ability wouldn't want to be playing in somebody's first team. And I would understand that."