The star defender was subbed off at half-time of the 2-0 win at Dundee on Wednesday because of a rib problem and is in doubt for this weekend's trip to Easter Road.
"Charlie has damaged a rib or pulled a muscle in the rib area," said manager Neil Lennon.
"He was finding it hard to breathe so he will have to be assessed. He was playing very well and had a great first half. That was an enforced change."