O'Brien was hopeful of a return by next month but an infection after an operation to fix the injury means he will now remain on the sidelines for the rest of the season.
He is also unlikely to bid to come back in time for Ireland's summer tour to Argentina - adamant he is better off focusing on the start of next season instead.
"I won't play until next season. There's no point in trying to rush back now before the end of the year or the summer tour," he said.
"It's probably a thing of starting a pre-season in a week or two, getting in good condition and getting ready for next year.
"It's looking good and I'm probably ahead of schedule considering everything that happened. I got a little infection in it a week after the op and had to have it cleaned out again.
"That set us back a week or two probably rehab-wise."