Darren Bent insisted he had to leave Aston Villa after too many "slaps in the face".
Brighton defender Greg Halford has agreed to extend his loan deal from Nottingham Forest until the New Year.
Papa Bouba Diop has not been offered a contract extension to remain with Birmingham.
The midfielder has been signing one-month deals with the midlands club since first arriving at St Andrew's in October.
He penned his latest one in mid-December having capped his only start for City with a late equaliser to salvage a 2-2 draw against Crystal Palace just days earlier.
But a hamstring injury means he has not featured for Blues since and City boss Lee Clark is unable to offer him another extension due to the cash-strapped club's financial struggles.
Diop, 34, made one start and one substitute appearance for Birmingham.