Neil Lennon revealed that Celtic skipper Scott Brown could be out for 10 weeks following their 2-1 Champions league defeat by Benfica at the Stadium of Light.
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The Hoops midfielder has been battling all season with a hip complaint, only playing intermittently and usually in the big games, but had to succumb to the pain in the second half when he was replaced by Kris Commons.
Parkhead boss Lennon said: "Scott Brown has run his course, we may have to book him in for surgery.
"We are looking at eight to 10 weeks.
"He has been pushing himself to the limit and we can't keep asking him to put himself through the amount of distress that obviously he was doing towards the end of his time on the pitch.
"He has been a huge player for us this season, I think it is time to get the problem addressed and hopefully he will have something to look forward to in the new year."
Lennon was alluding to the fact that Celtic's bid to win through to the knockout stages of the Champions League will go to their last Group G fixture.
Ola John gave the home side the lead in the seventh minute before Georgios Samaras levelled in the 32nd minute from a Charlie Mulgrew corner.
Defender Ezequiel Garay restored Benfica's lead in the 72nd minute to ultimately, and deservedly, leave both sides on seven points after five games.
The Scottish champions, guaranteed a Europa League spot after Barcelona beat Spartak 3-0 in Moscow earlier in the evening, will go through if, in their home game against the Russian club, they better the Portuguese side's result in Barcelona.
Lennon admits his last-16 hopes are in the balance.
He said "I think Benfica are capable of getting a win in Barcelona, for they are an excellent side.
"But we have to make them do that.
"I don't know what kind of mindset Spartak will be in, they might want to spoil our party, we have to be totally focused.
"What we have to do is win at home and make Benfica win in the Nou Camp which is no easy feat.
"The onus is on us to do that.
"The squad is stretched, we hope to have a few more players back for that game.
"No-one gave us a prayer coming in to this competition, these players have been exceptional, they have made a name for themselves and we are still in with a good chance of qualifying."
The former Celtic skipper had few complaints about the result.
He said: "I am disappointed. I thought there was a lack of composure to our play at times, a bit of nervousness which is understandable.
"Our passing was poor and we weren't decisive enough and it was a poor second goal to lose.
"We weren't at our best but you have to give credit to Benfica for the way they played."
Benfica coach Jorge Jesus will take succour from Celtic's win over Barcelona at Parkhead earlier this month when he takes his side to the Nou Camp.
Speaking about Tuesday night's win, Jesus said: "It was a great win for us. We didn't deserve to be drawing at half-time, they scored with a set-piece as we thought they might. But we played very well.
"Now we are playing on the biggest stage in the world against the biggest team in the world.
"But we have shown we are more of a team than Celtic and they beat Barcelona so nothing is impossible.
"If we have a bit of luck we can do it."
Celtic midfielder Victor Wanyama will miss the game against Spartak after picking up a booking in the second half.