The 27-year-old suffered the injury during a friendly against MK Dons last week and needs a scan to determine whether he requires surgery.
Blues boss Lee Clark told the club website: "It was absolutely ridiculous.
"It was so innocuous, it was 10 seconds from the end of the game as well, which is the frustrating thing.
"He sees a specialist this week who will decide whether he needs an operation or not."
- Sports & Recreation