Pompey are waiting to learn the full extent of Brian Murphy’s groin injury.
The keeper has been unable to train since being forced off at half-time with the problem against Accrington last weekend.
Paul Jones replaced him and remains in the frame for his first start of the League Two campaign when Barnet visit on Saturday.
The Blues’ medical team are still determining the damage to Murphy, who arrived on the eve of the season.
However, should the outcome be a lengthy period on the sidelines, it will raise questions over who will serve as back-up to Jones.
Michael Poke is currently on loan at Eastleigh, where he has been an ever-present in the National League.
Paul Cook had been keen for the 29-year-old – who was Jones’ understudy last season – to temporarily leave Fratton Park for games.
He has since made eight league appearances for Richard Hill’s side, who are second in the table.
The only other keeper on Pompey’s books is Alex Bass, who is currently in his final year with the Academy.
Bass appeared for Cook’s side in their final first-team pre-season match at Gillingham as a late substitute.
The youngster also lined-up against the Blues for Bognor in the summer as he attempted to clinch a loan move.
Meanwhile, Darryl Flahavan has been training with Pompey since July to keep himself fit.
The ex-Bournemouth keeper has been without a club since leaving Dean Court following 51 appearances.
The brother of late Pompey keeper Aaron, he previously spent the 2010-11 season at Fratton Park, without playing a game.