Birmingham's on-loan striker Obafemi Martins has been ruled out for the rest of the season with a leg injury.
The Nigerian, who last played against Wigan in March, has undergone surgery after suffering a stress fracture.
The 26-year-old, who is on loan from Russian side Rubin Kazan, scored City's winner in their 2-1 Carling Cup final victory over Arsenal in February.
"It's a blow for him and a blow for us and we wish him a speedy recovery," said Blues boss Alex McLeish.
"He passed his medical and everything was fine for six weeks but then it became obvious something was not quite right.
"The problem has crept up on him during the past month or so, and a stress fracture was diagnosed."
Birmingham were understood to have an option to buy Martins for around £4m when he moved on loan from Rubin.
He will remain with City until his loan spell expires at the end of May, but it remains to be seen whether the permanent move will now go ahead.
McLeish has said he will not talk about any deal until the end of the season.