Clark Robertson is set for a lengthy spell on the sidelines after suffering a hip problem.
The Pompey skipper recently saw a specialist on the issue that was picked up during a training session.
Danny Cowley has not put a timeframe on when the centre-back is likely to be fit enough to return to action.
But he revealed that fellow defender Connor Ogilvie could recover from a quad injury to feature at Charlton this weekend.
The Blues boss said: “We’re certainly hopeful for Connor. He’s made good progress and it looks positive for Saturday.
“Clark saw a specialist on Wednesday and now we have to make a decision on the best pathway for him.
"You’re always going to miss good players when they’re unavailable, but it’s up to us to find the solutions."
“But we do anticipate it being longer-term rather than shorter term. We’re hopeful he’ll be back before Christmas.
“It’s a ruptured tendon in the quadriceps and Clark’s a real loss because he’d been outstanding for us in the opening games.
“You’re always going to miss good players when they’re unavailable, but it’s up to us to find the solutions.
“There are two choices when you find yourself in these situations. You can become a victim or a fighter – we want to be the latter.
“Thankfully, we came through Tuesday night with no further fitness issues and everyone’s ready to go.”