All of this leaves the club in a somewhat awkward situation: could they really let O’Neill leave if he feels he still has the energy and the desire to continue?
Not according to a raft of ex-players and managers, who are all mightily impressed by the veteran’s achievements this season.
Former Ireland manager Stephen Kenny is clear on whether O’Neill should get the chance to stay on.
“The answer is yes,” he said. “You can’t do any more than he’s done. It’s an exceptional achievement. If he wants to do it, he should stay, and I don’t see why they wouldn’t keep him.”
No-one knows the demands of Celtic more than former club captain Scott Brown, who was more than happy to share his views on O’Neill.
“It all depends if he’s got the energy,” he said. “He’s talked about that in the past, it is burning a lot of energy. He’s getting a bit older. It’s up to Martin what he does.”
It may not be solely up to him, though. The Celtic hierarchy need first to decide in which direction they want to proceed – and with whom.
Should they decide to give O’Neill the option, let’s ponder one final question.
With a crack at the Champions League just one play-off tie away – and having answered Celtic’s call three times in his career – could O’Neill really resist a fourth and final spell?
