Celtic manager Neil Lennon fears Kelvin Wilson could be out for up to six weeks with an Achilles injury.
The defender was hurt in the 2-0 League Cup win over Ross County on Wednesday.
The former Nottingham Forest player is undergoing a scan today and Lennon said: "It looks like he has a slight tear in the Achilles.
"It depends on the significance of the tear. We are hoping that it will be at best two to three weeks, it could be four to six weeks."
With Charlie Mulgrew suspended for Saturday's Scottish Premier League meeting with Inverness, Lennon will need to reorganise his defence.
Full-back Mark Wilson is available again after missing the visit to Dingwall, while forwards Georgios Samaras and Paddy McCourt have also shaken off knocks.
However, midfield pair Kris Commons and Scott Brown remain on the sidelines.
"Kris Commons is also definitely out and it is touch and go whether Scott Brown will make the Hearts game next week," explained Lennon.