Skysports.com understands Birmingham risk losing star duo Scott Dann and Roger Johnson after putting off contract talks with the pair.
Dann and Johnson have established themselves as one of the best central defensive partnerships in the Premier League after joining Birmingham in the summer of 2009 from Coventry and Cardiff respectively.
The highly-rated duo played a key role in helping Birmingham secure survival in the Premier League last season and are seen as the cornerstone of Alex McLeish's side.
The consistent performances of Dann and Johnson has attracted interest from other Premier League clubs and also lead to calls for the pair to be included in the England set-up
However, both players are thought to be unhappy with the club's failure to offer them new long-term contracts as a reward for their progress.
It is believed Birmingham were ready to open contract talks with both players before the start of this season, but McLeish wanted the club to wait until October before sitting down.
However, those discussions have yet to take place, much to the disappointment of Dann and Johnson, who have both just over two years to run on their current contracts.
Sources close to the duo say the players feel let down by the club that they have not kept promises they made over their contract situation.
The situation is believed to have caused major unrest within the Birmingham camp with the duo thought to be two of the lowest earners at the club compared to other members of the squad.
Birmingham would be loathe to lose the defensive kingpins, but could face a fight to keep hold of them if they do not secure their long-term futures on new terms.