Celtic midfielder Shaun Maloney will be sidelined for up to four months after undergoing ankle surgery.
The 27-year-old had been captaining the side in the absence of Scott Brown, who has been injured since mid-October.
Celtic last played on 27 November and Maloney was taken off after just nine minutes of the 2-2 draw with Inverness.
Manager Neil Lennon also revealed that central defender Glenn Loovens would be missing for a month with a medial knee ligament injury picked up in training.
Maloney was hurt after his close-range shot was smothered by Inverness keeper Ryan Esson.
"He had surgery on Monday," explained Lennon. "It was a simple procedure but he will be out for a length of time.
"We are looking between three and four months. It's a huge blow for us and obviously a huge blow for the player."
The diminutive Scotland international did not play after October last season after being struck by an tendonitis problem in his ankle before suffering a number of niggling injuries.
He also missed four months of the previous season with a persistent hamstring problem.
"He was starting to show his best form this season," added Lennon.
"He had a horrendous run of injuries in the previous season.
"It is frustrating obviously because he worked very, very hard to get back to full fitness when he has been out.
"This is not a soft tissue injury, it is a trauma that he picked up against Inverness.
"It was early in the game as well and on conclusion it was decided that surgery was required."
With Brown and Maloney missing, manager Neil Lennon is likely to make defender Daniel Majstorovic his skipper.