Defender Daniel Majstorovic has been ruled out for up to three weeks, Celtic have confirmed.
The 33-year-old Sweden international has played in every SPL match this season since moving to Parkhead from AEK Athens last August, missing only the season-opener with Inverness.
However, Majstorovic picked up a hamstring strain and was forced to come off during the first half of last Saturday's 1-0 defeat of Aberdeen.
A statement on the club's official website read: "Following a scan today, it's been confirmed that he'll be out for up to three weeks."
The confirmation of Majstorovic's spell out could lead manager Neil Lennon to try to speed up Kelvin Wilson's move to Parkhead.
Nottingham Forest defender Wilson has signed a pre-contract with Celtic and will move north at the end of the season.
However, with Jos Hooiveld away on loan at FC Copenhagen and Glenn Loovens making his way back from injury, Lennon could try to persuade Forest to release the player early, even if it involves a fee.
Following Saturday's game with the Dons, the Celtic boss said: "It is a blow if Majstorovic is out because he has been immense in the last couple of months for us.
"We will have to try and get someone of that ilk in. I would imagine that Wilson will be one of the options we look for, yes."