He missed Saturday's 3-1 home defeat to West Brom and will also be absent from Wednesday's clash with Everton at Goodison Park.
But Ferguson has agreed to undergo a painkilling injection later in the week in a bid to be fit enough to rejoin Blues' battle to stay up.
Blues manager Alex McLeish said: "If we were in mid-table, like at this stage last season, we would definitely not play Barry. But he wants to play. Barry said he can't sit about, he just wants to play."
He added: "He has volunteered to take the injection. I think it will happen later in the week to allow things to settle down.
"There's not much you can do in terms of strapping up ribs and things like that, but the injection kind of freezes that side of his rib cage and gives it protection.
"It's Barry's decision, definitely. He did something similar when at Rangers.
"He's a brave boy. He showed his pain threshold in playing for an hour of the Carling Cup final with the injury."
Source: PA
Source: PA