Matthew Upson could spark a major bidding war after the player's agent revealed the player will not be signing a new deal at Birmingham.
The former Arsenal star is being chased by a number of clubs including Liverpool, Portsmouth, Tottenham and Aston Villa as he looks to leave St Andrews.
Upson's current contract expires in 18 months' time and Birmingham are prepared to consider a sale for the right price.
The player's representative Barry Nevill confirmed Upson was seeking to move on and would turn down Birmingham's offer of a new deal.
"Matthew will not be signing a new contract at Birmingham," Nevill told the News of the World.
"He believes his future lies elsewhere and has ambitions to play at the highest level.
"Even if Birmingham make him an offer he can't refuse ... he will refuse it!"
However, Blues chairman David Gold is not giving up hope of keeping Upson at St Andrews and believes the central defender can achieve his ambitions at the club.
"He is desperate for success," said Gold. "Yet unless one of the top four come in for him, he has as much chance of achieving it here, once we are back, as with any other Premiership club.
"But if we get the right offer, we'll consider it."