Birmingham's on-loan defender Tom Thorpe has returned to parent club Manchester United for treatment after sustaining ankle ligament damage on his debut.
Thorpe arrived at St Andrew's on transfer deadline day on a deal until the end of the season and duly made his bow in Saturday's home clash against Derby.
However, the centre-back lasted just 15 minutes of the 3-3 draw before leaving the field on a stretcher, adding to Blues' defensive woes following the loan recalls of Kyle Bartley and Dan Burn.
It remains to be seen how long Thorpe, 21, will remain on the sidelines, although City will be kept updated on his progress.
Manager Lee Clark told the club's official website: "We're devastated for him.
"He's a terrific kid and we were absolutely delighted to get someone of his quality. Manchester United rate him so highly and he's been a brilliant lad."