Sky Sports News understands Birmingham have made an approach for Aston Villa's Curtis Davies.
The defender appeared to be on his way back to Leicester on Tuesday, revealing on his personal Twitter account that a return to the Foxes was imminent.
It was expected that Leicester, who were impressed by Davies during a loan spell earlier in the season, were keen to take the 25-year-old in a deal which would be made permanent in the summer.
However, those plans may have been scuppered by Birmingham, with the Blues having now entered the race.
It is understood that initial contact has been made by Birmingham regarding a deal and they are now waiting on further progress.
Alex McLeish has set his sights on Davies after seeing Scott Dann sidelined for the remainder of the season with a hamstring injury.
He has identified defensive cover as a priority in the January transfer window and feels Davies could be the ideal candidate.
Birmingham will also believe that they are now the frontrunners to strike a deal, with the former West Brom centre-half having revealed in the past that he would prefer to remain in the Premier League.