Brendan Rodgers has confirmed Cameron Carter-Vickers will be sidelined until after the winter break.
The Celtic boss admitted his side will be without the USA international against Rangers tomorrow.
And he will also miss the match against St Mirren on January 2.
Carter-Vickers had suffered a hamstring knock in the 3-0 win over Dundee on Boxing Day.
Early signs suggested the defender hadn't taken a serious injury blow - however, he will now be sidelined until into mid-January at least.
Carter-Vickers missed training with his team-mates on Friday ahead of the clash with Rangers before Rodgers confirmed the worrying injury news.
On Carter-Vickers' injury, Rodgers said: "I always think it is an opportunity for someone else, we had it in the last game when Gustaf and Liam Scales came into the team and for Liam it was the making of him.
"It's always a sadness whenever you lose a top player but like I say, hopefully it's not too long a time, he'll be back after this break and then hopefully he'll stay clear of injury for the second part of the season."
However, Celtic did receive some fitness boosts in the return of Liel Abada and Reo Hatate to full training ahead of the derby encounter on Saturday.
The pair were fully involved at Lennoxtown and looked fit to feature at Celtic Park.
And Rodgers said of the duo: "They've trained, and Liel a little bit longer.
"We don't want to rush them but if they come through well today then they'll be involved in the squad for tomorrow."
