Celtic forward Daizen Maeda faces six weeks out after suffering a knee injury in the challenge that earned him a red card against Atletico Madrid.
Maeda was initially booked following a 50-50 with Mario Hermoso but the yellow card was upgraded to a red following a VAR review.
The Japan attacker had left a leg dangling and Hermoso went down in dramatic fashion after catching Maeda’s studs as he followed through.
Manager Brendan Rodgers said: “Daizen will probably be up to six weeks out with the injury from the challenge. He has strained his medial knee ligament which comes from when you just knock a player on the foot.
“If he was in stronger in the challenge he probably wouldn’t have had the injury. The clash of feet has just opened up the knee ligament.
“It’s a big shame for us because he has been brilliant for me since I came here.
“It’s a big loss because his attitude and mentality going into every game is superb. He initiates the pressure for us at the top end.
“It’s a real shame because he has been like a machine since he came to Celtic, watching him before I arrived and then coming here and seeing what he does every day and in the games, he is incredible. He hasn’t had too many knocks.
“But I always say, it’s an opportunity for someone else to come in and play.”
The injury blow compounded Rodgers’ frustration with the decision to send Maeda off in the 6-0 Champions League defeat.
“You only have to assess the incident. Everyone could see if you know football at all that there was no intention, he was just overstretching and both players clash feet,” he said.
“The irony is that as soon as the red card went up, their player miraculously got up off the floor.”
Rodgers remains calm about the nature of the defeat given Maeda’s red card midway through the first half had such an effect on the game – and he will not give up trying to make Celtic more competitive at Europe’s elite level.
“You always have to dream we can do that,” he said. “That’s what being a coach, manager, player, supporter is. If I thought there was never any hope there is no point in doing it.
“My dream is always for Celtic to be at the very highest level in European football. It’s very, very difficult but that won’t stop us, we have to keep fighting and keep looking to develop the squad to challenge the level.
“We played them at home and were very close, amazing support pushing us, fantastic performance.
“But the Champions League level is about quality and especially at the top level of the field.”
Rodgers, whose team host Aberdeen on Sunday, added: “For us it’s a continuation of fighting, running, working and developing players to have the belief at that level.
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“Look at Matt O’Riley, two years ago he was playing in League One. Other young players like Liam Scales are sampling it and have thrived in it this year.
“But what you can’t do is give them experience and that comes from being in the competition and it comes from adverse moments as well because adversity helps you learn.
“My overall feeling after reflecting and debriefing, for us to have gone there and felt we could get a result against a team who will go deep into the competition, I think it tells you everything about how well the team had done up to that point.
“It was just unfortunate the sending-off culminates in a heavy loss.”