Aston Villa midfielder Birkir Bjarnason faces an extended period on the sidelines after undergoing groin surgery.
The Iceland international has not played for Villa since being forced off injured in the 1-0 defeat to QPR on October 26.
Bjarnason posted a photo on Instagram from his hospital bed, with a message which read: "Surgery went well. I'll be back stronger than ever."
He started the first three games after Dean Smith became manager but missed the 2-0 home win over Bolton and the 3-0 victory against Derby at Pride Park before the international break because of the problem.
The 30-year-old also had to withdraw from the Iceland squad for their recent games against Belgium and Qatar.
Watch the Second City derby on Sunday. Coverage of Aston Villa vs Birmingham begins on Sky Sports Football at 11:30am.