Brett Pitman’s hamstring injury will sideline him for Saturday’s visit of Plymouth Argyle.
The problem ruled Pompey’s top scorer out of last night’s trip to Peterborough United, prompting a recall for Curtis Main.
In his absence, Kenny Jackett’s men slipped to a 2-1 defeat – halting a three-match winning streak.
The Blues struggled in the final third during the League One encounter, although did net a 78th-minute consolation through substitute Conor Chaplin.
Pitman, who collected the injury in last weekend’s 1-0 victory over Southend United, will also be absent from the Pilgrims’ visit.
However, boss Jackett does not believe it is a long-term problem for the former Ipswich Town and AFC Bournemouth hitman.
He said: ‘Brett felt his hamstring on Saturday.
‘It isn’t too bad but he wasn’t available last night because of it and won’t be available against Plymouth.
‘We are hopeful that next week it will be okay.
‘We will certainly assess it after Saturday’s game. He’ll need some time off.
‘Hopefully by the time the next league match comes around after Plymouth he will be okay.’
Main was handed only his third league appearance of the campaign to fill the gulf created by Pitman’s absence.
Operating as the lone striker, he struck the outside of the post during a first half in which the Posh’s Gwion Edwards hit the bar.
Main was replaced in the 64th minute by Chaplin, who netted his third goal of the season after Danny Rose’s intial effort was saved.
And Jackett explained his reasoning for starting Main over Chaplin.
Pompey’s boss added: ‘We wanted to try to go like-for-like size-wise, so gave Curtis a go.
‘In the games he has played he has played very well and hasn’t had many chances or opportunities for us. His last league appearance was at Gillingham where he played very well.
‘Curtis was unlucky in the first half.
‘He’s had a good shot and struck the post and it would have been nice if that had gone in.
‘I also felt Conor came on and did very well again and I am pleased for him getting the goal.
‘There were one or two situations where he was disappointed and maybe would have looked to have done better as well.
‘But he’s a very capable player and one I am looking at.’