Brendan Rodgers has revealed that Daizen Maeda will be out of action for up to six weeks.
The Japan international was sent off during the 6-0 defeat to Atletico Madrid and the Parkhead boss confirmed that the injury occurred due to the challenge.
Maeda is now likely to miss the remaining two Champions League fixtures against Lazio and Feyenoord.
He also faces a race against time to be fit for the derby against Rangers on December 30.
Rodgers said: "Daizen will probably face up to six weeks out with the injury from the challenge so he has strained his knee ligament which comes when you knock a player on the foot.
"If we went in stronger in the challenge then he probably would not have the injury so it was a clash of feet that just opened up his knee ligament.
"It is a shame for him and for us because he has been brilliant."
Meanwhile, Tottenham boss Ange Postecoglou has opened up on his stubborn tactical approach during a discussion with Manchester United hero Rio Ferdinand.
The Australian was presented with evidence of his Celtic side pressing away to Real Madrid last season and he detailed his thinking behind the tactical approach.
The Hoops lost 5-1 in Spain but the 58-year-old explained why he no had intention of changing his approach despite the opposition.
Ferdinand told TNT's Between the Lines: "This is Celtic against Real Madrid at the Bernabeu. I can sense how strong you are of your principles and the way you play.
"Even when you're playing against a star-studded team, you're going to go for it and play the way you want to play. You get beat here 5-1 but you're still going for it."
Postecoglou responded: "Yeah, we pay a heavy price. This is what I'm saying, this is where the tests come where the players are looking at me and saying 'well, if we're going to change against Real Madrid then you don't really believe'.
"The challenge for Celtic then would have been can we progress from just being really aggressive and we had these moments where we won the ball but didn't have the quality to finish off and hurt a team like Real.
"The question is 'Can we keep doing it, where we can improve that quality in the front third'.
"I think the players got comfort from knowing irrespective of the scoreline I would take the flak for the 5-1. If we keep doing this, we'll get the rewards at some point."
