Andy Awford has revealed Alex Wynter is still suffering the effects of his bump to the head.
But the Blues boss is convinced he has enough right-back options.
Wynter has not trained since coming off against Peterborough after taking the blow.
In his absence, Adam Webster has featured until his suspension.
Ricky Holmes then played as a stand-in right wing-back for the last two fixtures.
Against Oxford, Holmes had to be substituted at half-time having been booked and in danger of being dismissed.
With Webster left out of the squad, it was Jed Wallace who stepped into the role.
Pompey now head to Stoke tomorrow in the Capital One Cup, but Wynter is again set to miss out.
He said: ‘Alex Wynter is still a bit groggy after his bump on the head.
‘He has not trained and I haven’t got a clue when he can until the medical people tell me.
‘With Adam (Webster), I felt it was the right thing to do to leave him out against Oxford and give him a breather after last week.
‘I wanted to take him right out of the firing line and get his head right, ready for the next batch of games that come.
‘But you have still got enough to play there, if we wanted to go for a four or even a five at the back I could have put Joe Devera out there,
‘Obviously Ricky is not used to playing there.
‘It’s not his favoured position, we all know that, we want Ricky higher up the pitch getting at full-backs or playing off the front.
‘But if you ask him to do a job then he steps in and does it to the best of his ability.
‘It’s not his favourite position, of course it isn’t, but he can play there.’
Webster will come into the frame for the Britannia Stadium trip.
As will Holmes, who was tactically substituted on Saturday.
He added: ‘It was the sensible thing to do and Ricky understands that.
‘I was thinking about doing it before half-time because they were on at the ref, it was an intense atmosphere with the crowd as they are and one more challenge from Ricky and he’s off.
‘I just felt it was the right thing to do.’