The coach will make a late decision on whether to select him for the Valentines Day clash in Paris.
"We always knew that Brian's case was going to go down to the wire," said O'Sullivan.
"I'm not trying to say he's going to be fit when he isn't, we really don't know.
"I want him to play in Paris because he is a class player and the skipper of the team. But if he aggravated the injury because we've brought him back too early then it will be a mistake on my part.
"We want to give him every opportunity to play in Paris but we won't take risks.
"The decision will be made in the middle of next week at the earliest and I'm happy to leave it that late."