Ben Coker ruptured two knee ligaments in last weekend's game against Sunderland and will be out for an extended period.
The news comes as a further blow to Blues after Tom Hopper was ruled out on Monday for the remainder of the season with an ACL injury.
Coker will undergo surgery imminently and will now also be out for the rest of the season.
Blues boss Chris Powell said: “It’s a devastating blow, on top of what we’ve had recently, to lose Ben in such an innocuous way. I watched the video today and nobody is near him.
“We’ll miss him but it’s all about his health and getting him back to the level. He will work hard to achieve that and we will be alongside him all the way.”
The club would like to wish Ben a full and speedy recovery as he begins his road to full fitness.