Brentford have now agreed a deal with Birmingham for Maxime Colin, after originally knocking back the Blues' first offer.
The Frenchman will be the third player to move to the west Midlands in just over 24 hours, following centre back Harlee Dean and winger Jota.
Birmingham had made an early offer, which was turned down by the Bees, however they have now produced one that matches the club's valuation.
Colin first moved to Griffin Park in the summer of 2015 and his season was interrupted by injuries.
He was a regular last season but has found himself deployed at left back due to an injury to Rico Henry and the arrival of Henrik Dalsgaard.
The Bees will now have to consider whether they return to the transfer market to bring in a full back, given Henry's injury concerns, or promote Ilias Chatzitheodoridis to the first team at left back.
Josh Clarke is also capable of playing for the Bees at right back were Dalsgaard to suffer an injury.
