The former Swedish international left the field after colliding with Gustave Bahoken in the 14th minute and was rushed to hospital.
Larsson will definitely miss the big games against Stuttgart in the UEFA Cup and Rangers in the CIS Insurance Cup final and Scottish Premier League.
The news is a big blow to the Celtic boss. “He will be operated on tonight,” confirmed O’Neill. “I’m not sure the length of time (he will be out for). It looks like he’s had a double fracture of the jaw so to win despite that was a fantastic effort.”
O’Neill confirmed that the 34-goal striker will miss the forthcoming games with Stuttgart and Rangers, but he is refusing to rule him out for the rest of the campaign.
“I really don’t know how bad it is at the moment,” continued the visibly-shaken Celtic manager.
“He will be operated on tonight. I would hope that he will come back before the end of the season to be perfectly honest.
“Sometimes these operations go so well, and I’m only guessing but I’m hoping that it is going to be weeks rather than months.
“But knowing Henrik he came back from a broken leg and I think he will come back as quickly as possibly. It’s a major blow to us because he is a world-class player.”
Celtic did cope without him against Livingston and it was his replacement Shaun Maloney, whose free-kicks led to Momo Sylla’s equaliser and Chris Sutton’s late winner after Rolando Zarate had threatened to dent the champions’ title aspirations.
“It was an absolutely fantastic effort from the team considering we lost Henrik so early in the game,” said O’Neill.
“I thought the whole team’s response was terrific and Shaun took a bit of time to settle down for the first few minutes.
“His first few touches went away from him and it took him time to get to the pace of the game, but his own performance was sensational.
“The whole team responded well to going a goal behind. Livingston caused us a few problems, but eventually it was a magnificent win and Shaun was instrumental in it.”
O’Neill reacted angrily to claims over the weekend that he met with Leeds United chairman Peter Ridsdale over the possibility of becoming their manager in the summer.
The Northern Irishman is supposed to have agreed to the move and then had a dramatic change of heart, but that question sparked an angry reaction from him.
“I signed a three-year contract here with the football club,” snapped O’Neill. “I have honoured every single one of the terms and conditions of that contract.
“I am telling you now that I honoured that contract and that’s my final point on the subject today.”
CELTIC: Hedman, Valgaeren, Balde, Laursen (Guppy 57), Sylla (Lambert 85), Lennon, Petrov, McNamara, Smith, Sutton, Larsson (Maloney 17).
LIVINGSTON: Main, Brinquin, Andrews, Rubio, Maidana (Bingham 78), O’Brien, Quino, Bahoken, Lovell (Amor 64), Zarate (Wilson 62), Dadi.
Referee: M. McCurry.