Midfielder Dariusz Dudka has left Birmingham having failed to earn an extended contact at St Andrew's.
The Poland international, 30, arrived as a free agent at the end of October and penned a short-term contract until January 1.
However, he made just one start and one substitute appearance during his two-month stay at the Championship club.
"These sort of short-term deals are always difficult when you bring in a player who hasn't played or trained much because of their circumstances," Clark told Birmingham's official website.
"He's obviously an international footballer and has got a lot of quality. But after speaking to him when he made his full debut against Middlesbrough he actually realised how quick the level is in the Championship in comparison to where he's been.
"I'd like to thank Dariusz for the contribution he made during his short time with us and wish him every success in his footballing career."
Dudka is an experienced international for Poland having racked up 65 caps and featured in the 2006 World Cup as well as the 2008 and 2012 European Championships.
He played for French club Auxerre and more recently Spanish side Levante, whom he parted ways with last summer.