Jack Whatmough has undergone a successful knee operation.
The defender was in London over the weekend for surgery after getting injured in the Fratton draw with Doncaster earlier this month.
Head physio Bobby Bacic said: “The operation took place on Saturday morning. It was a microfracture procedure, with a synthetic membrane then placed over that.
“Everyone’s been asking how long he’s going to be out for and I think we’ll give it up to a year for his rehab.”
"I’ll always back Jack and believe he has the courage to get over this setback."
Blues boss Kenny Jackett added: “The most important thing is that the operation was successful and Jack recovers.
“It’s well-trodden path for him, but he’s a determined lad and we’ll all be supporting him 100 per cent.
“He has the determination to get through the long road of rehabilitation. I’ll always back Jack and believe he has the courage to get over this setback.”