The forward lasted just 45 minutes of the Blues' derby date with Aston Villa on Sunday before being forced off.

Scans have since revealed that the Scotland international has torn a muscle in his thigh and will require a spell on the sidelines in which to recover.

Early indications suggest McFadden could miss Birmingham's next five matches, while he will also be forced to sit out an international friendly against Japan in October.

The news comes as a major blow to Blues manager Alex McLeish, who has seen his side make a mixed start to the new campaign.

"It's a big blow for us because he has been in great form since the start of the season," said McLeish.

"I'm not going to put any targets on his return. He will be back when he's back, but we have lost him for the foreseeable future."