Stephen Henderson is set for a lengthy spell on the sidelines.
The goalkeeper made his second debut for Pompey in Saturday’s 2-2 draw with Doncaster after completing a deadline day loan switch from Nottingham Forest.
But he limped off with a thigh injury in the 85th minute, meaning Kal Naismith went between the sticks for the closing stages.
And Kenny Jackett has confirmed that Luke McGee will now be handed another opportunity to impress.
The Blues boss said: “It’ll be months rather than weeks. It looked quite bad at the time and I haven’t heard anything to suggest otherwise.
“It does happen to every club. Unfortunately, you pick up injuries and it’s certainly not exclusive to us. You just have to adapt to it.
"It looked quite bad at the time and I haven’t heard anything to suggest otherwise."
“I’m pretty sure he’ll stay here and see what the next month brings. He’ll be frustrated, but now he has to focus on getting fit.
“Luke has consistently played throughout the season. He probably didn’t think he’d get his next chance so quickly.
“I expect him to bounce back and work hard to keep the shirt because he’s a very good character.”
Jackett also has no complaints about dismissal of Christian Burgess in stoppage-time, with a handball earning the defender a second yellow card.
He said: “I’ve seen it again and I can’t argue with the referee’s decision because it was a bookable offence.
“From that point the team battled really well and I have to say they were aided by a magnificent crowd.”