Carlisle skipper Paul Thirlwell will be sidelined for a month after straining a medial knee ligament.
The 31-year-old midfielder sustained the injury in last weekend's 1-0 win at Sheffield Wednesday and scans have since confirmed the full extent of the damage.
Cumbrians physio Neil Dalton said: "Paul came into work on Monday morning and the knee was stiff, so we sent him for the scan.
"That confirmed that the medial ligament was sprained and we expect him to now be out for three to four weeks.
"He has had treatment this week and his rehab will continue as we work towards getting him back on the training ground."