Carlisle boss Greg Abbott concedes he may be forced into the transfer market after losing Danny Livesey to injury for the first month of the season.
The influential centre-half, who recently signed a new two-year deal, has been ruled out for up to eight weeks after suffering a groin injury in training.
Abbott, who was already in the market for a centre-half after Tom Aldred's departure to Watford, is now stepping up his bid to sign new defenders before the season starts on August 7.
"Danny's injury is the one downside of our pre-season so far and we might be in the transfer market now," Abbott told the News & Star.
"We are actively trying to improve the squad."