Jonathan Spector has become the latest player to commit his future to the club.
The experienced American international has penned a new two-year contract that runs until June 2015.
The 27-year-old joins senior players Paul Robinson, Wade Elliott and Colin Doyle in signing new deals.
Spector, who is predominantly a midfielder, but can operate in defence, has been with Blues since his move from West Ham in 2011.
To date, he has made 76 appearances and scored a solitary goal.
Boss Lee Clark sees Spector’s decision to re-sign as a real fillip to his squad rebuilding plans.
“Jonathan signing is a big boost and I’m looking forward to having him back in the group and being part of the squad,” said Clark. “He was the last one of three lads that were out of contract to commit to the club.
“In terms of football he’s still young, but he’s a very experienced player in terms of the games he’s had for a player of his age.
“His versatility is a big thing for us because he can cover different positions. As well as midfield he can play as a full-back, although I ultimately think that as he goes on he could be a decent centre-half because he’s an aggressive player, he’s got good aerial ability and he’s mobile.”