Derby defender John Brayford is facing six weeks out after sustaining a thigh injury, manager Nigel Clough has revealed.
The defender limped off in the 58th minute of Saturday's 4-0 defeat at Southampton after suffering the damage.
The Rams have confirmed the 24-year-old has torn a muscle in his thigh after he underwent an MRI scan on Monday.
Manager Clough does not expect Brayford to be back in action until the beginning of April.
"It doesn't look too promising, so he will be missing for the foreseeable future," he told the Derby Telegraph.
"If it is six weeks, which is the norm for this sort of injury, obviously that puts us quite close to the end of the season.
"It's a big blow."
Brayford has suffered problems with the same thigh earlier in the season, spending two months on the sidelines between October and December.
He was also out for two matches before the trip to St Mary's and Clough added: "We look back now and wish we could have left him for that extra few days but there is no way of telling this would happen.
"It (his thigh) might have gone against Leicester City on Thursday or next week, or whatever."
Clough says midfielder Paul Green is likely to fill in for Brayford at right-back when Leicester visit Pride Park in the Championship on Thursday night.
Young stopper Tom Naylor is also in the manager's thoughts to cover for the defender.
"Tom can play right-back and has done in the reserves a few times," said Clough.
"It might be a bit much to throw him in at this particular moment, so Greenie will probably deputise there on Thursday.
"We have been pleased with Tom's progress. If we had another five or six points on the board we might well throw him in and keep Greenie in midfield."