Pompey are waiting to learn the full extent of Oli Hawkins’ injury.
The recently-converted centre-half was forced off in the 59th minute of last night’s 4-0 Carabao Cup defeat to Southampton.
Hawkins, who once again impressed in the role, was replaced by Paul Downing, with the score 2-0 at the time.
Boss Kenny Jackett afterwards revealed the 27-year-old had sustained an injury to the bottom of his left foot.
Following the match, Hawkins departed Fratton Park wearing a protective boot.
His season has already been wrecked by injury problems, an absence stretching back to the summer.
And Jackett admitted he is awaiting news on the former Dagenham & Redbridge man’s latest setback.
Pompey’s boss said: ‘The injury to Hawkins is a frustration for me and hopefully he is not out for too long.
‘He has a problem with the bottom of his foot, it’s a different one to the other foot injured earlier in the season.
‘I don’t know how long he will be out for, it’s a really difficult one, but obviously he felt it and was in too much pain to carry on.
‘His substitution was a frustration, I thought Hawkins was outstanding, as he was on Saturday, and I hope he is soon over his injury.’
Southampton ran out comfortable winners at Fratton Park, with goals from Danny Ings (two), Cedric and Nathan Redmond.
Pompey next entertain Bolton on Saturday, with the injured Hawkins expected to missing the south-coast clash.