Lee Brown has undergone surgery on his Achilles injury after seeing a specialist.
He now joins fellow left-back Brandon Haunstrup – who required an operation on his meniscus – on the sidelines.
But Kenny Jackett can at least welcome back two members of his defence that missed last week’s defeat at Accrington.
The Blues boss said: “Lee’s had an operation on his Achilles and we hope that it will be a successful one.
“We think with both him and Brandon, it’ll be at some point in February when they’ll both be available again.
"We think with both him and Brandon, it’ll be at some point in February when they’ll both be available again."
“The balance of left footers in the squad – and left-backs in particular – is something we’ll need to address.
“Christian Burgess is back after his one-game ban and Oli Hawkins is also available following the birth of his first child, so they’ll join the group that went up to Accrington.”
Jack Whatmough took part in a training ground friendly match on Thursday morning, as he continues his comeback from a long-term injury.
Jackett said: “We think we’ve thrown everything at him to test that knee out and he’s come through all of it.
“That’s really good news and, as he passes each test, the time for him to return gets ever nearer.”