Steve Cotterill doesn't believe Hermann Hreidarsson is ready to solve his defensive crisis.
Pompey have shipped three goals in each of their past four matches as their back line has crumbled dramatically.
And after 28 games this term, the Blues have managed only three clean sheets.
It is an alarming statistic made even more concerning with fixtures against promotion-chasers Nottingham Forest, Leeds and QPR on the horizon.
At Brighton on Saturday, Ibrahima Sonko was chosen to partner Aaron Mokoena in the centre of defence in place of the injured Ricardo Rocha.
Instead, Hreidarsson came on as a half-time substitute, slotting in at left-back.
Since the Icelandic international's return from the career-threatening Achilles injury he picked up against Spurs last March, his sole start has been the Boxing Day draw against Millwall.
In addition, he has climbed off the bench seven times, although most have been in the final few minutes of games.
But despite Pompey's defensive woes, Cotterill remains reluctant to turn to the veteran at this moment in time.
He said: 'I am sure Hermann has still got a long way to go before he's back to what he would be.
'He might only get that before the end of the season because he's had a few months of it.
'With him and Danny (Webber) we could have had two other players who have played in every game and played 48 matches between them by now.
'Instead, we've got about one-and-a-half games out of two of them.
'That is what happens with long-term injuries. And the thing is, when they come back they don't always drop back into what they were.
'I don't think Hermann is ready to start a game yet, no. I can't lob him in and say "on you go then and it doesn't matter if you make a mistake".
'That is the difficulty with the size of the squad and not having a reserve game.
'We tried to arrange some games before Christmas that hopefully would have helped.
'On a couple of occasions we ended up having some XI versus XI out there with some younger players, the kids and Woany (Ian Woan) and Guy (Whittingham) joining in.
'Hermann is not as fit or as ready as the other three (Sonko, Mokoena, Dickinson) are for playing. The others are still advanced, 100 per cent.
'He probably wants to be there and be ready and all of that, but that can't be his choice, that has got to be somebody else's choice.
'You always think you are right. Sometimes when you are coming back from injury you don't think there is anything different in you.
'But I for one don't think he's there yet.'
Danny Webber has still to return to full training as he nears his comeback.
The striker has been out since March last year after sustaining cruciate ligament damage in the same Spurs game as Hreidarsson.
The likelihood is he will be training with his colleagues by the end of this month.
That will be a massive boost for Cotterill as he continues to be prohibited by his paper-thin squad.
With a substitutes' bench containing just four players in two of the past three matches, any additional options represents a big bonus.
Cotterill added: 'We need all the bodies we can get.
'Even over the past few games with Hermann, we have had two players registered to us who basically haven't kicked a ball.
'They've had long-standing injuries, the pair of them.
'At the end of last week, Danny was out on the grass doing proper football stuff, but he is not with the group yet.'
Pompey have rescheduled their clash with Burnley.
The Fratton Park fixture has been arranged for Tuesday, January 25 (7.45pm).
The match was originally set to take place on December 4, only to fall victim to snow and ice. All tickets for the original game are valid.
A date has yet to be announced for the rearranged game against Scunthorpe which also fell foul of the weather.