Gary Roberts has been ruled out of Pompey’s trip to Oxford United.
The influential midfielder has ligament damage to his right ankle following Sam Togwell’s first-half challenge against Barnet.
Paul Cook believes Roberts could now be sidelined for the two weeks, ensuring he is out of Saturday’s trip to the Kassam Stadium.
The Blues then travel to Bristol Rovers on September 26, before Exeter come to Fratton Park on September 29.
But Pompey’s boss insisted the 31-year-old was doing all he could to return to action ahead of schedule.
He said: ‘Gary got the kick on his ankle in the first half, he wanted to carry on but he had gone over on it.
‘He went for a scan and it was a grade one tear in one of the ligaments, the likelihood is he will be out for a couple of weeks.
‘Knowing Gary he might make Bristol Rovers. He is a lad who wants to play, he’s been challenging Sean Duggan (Pompey physio) to play this week, but that’s Gary.
‘He’s doesn’t want to miss any games and is keen on getting it strapped up to play, but he hasn’t noticed how well he is playing!
‘In our 4-2-3-1 we have Kal Naismith ready to play, Gareth Evans can come back into the team and Ben Tollitt is training really well, so we have good options to replace him.’
Roberts has made seven appearances for the Blues, scoring three times.