Richie Barker has conceded he does not possess the personnel to employ a ‘successful’ 4-4-2 system.
The Blues boss is concerned the squad he has inherited is lacking sufficient balance for certain formations.
That has prompted him to operate with a 4-2-3-1 line-up during the past three matches, from which the Blues have taken four points.
It’s a switch he has deemed necessary having witnessed defeats against Newport County and Bristol Rovers in his opening two matches as Pompey manager.
Crucially, first-choice central midfielder Simon Ferry has also been absent for the last two matches with a recurring hamstring injury.
Barker is currently attempting to improve his squad during the transfer window to help his side climb the table.
But despite some fans favouring a 4-4-2, he does not feel able to implement it effectively at present.
He said: ‘You have to play to the personnel you have, to be successful.
‘And I would say we cannot play 4-4-2 at the moment.
‘It is a conversation I have had with various others and I don’t want to say too much because I might upset people.
‘In the game the other day (Northampton) people were wanting a 4-4-2 – and I understand that feeling, that is their view and I respect that.
‘But if you have not got the personnel to do it, then it’s not something you can introduce.
‘You could make changes from the bench but again playing 4-4-2 is an issue and it could end up costing you the game.
‘Sometimes you have to play a certain way at certain times and we are currently going 4-3-3 or 4-2-3-1.
‘At present, I just don’t think we can play 4-4-2 to be successful in getting results we need.’
Barker’s tactical change came into play after the dreadful display at Bristol Rovers before Christmas.
As a result he changed from the 4-4-2 system and secured a 1-0 victory over Dagenham & Redbridge.
The following match some fans chanted ‘4-4-2’ and wanted the introduction of David Connolly during the goalless draw with Northampton.
Connolly was introduced with seven minutes to go, partnering fellow substitute Ryan Bird in attack.
The Blues then gave an impressive performance at Southend with the 4-2-3-1 formation. It was a game they were unfortunate to lose.
They travel to promotion-chasing Oxford on Saturday, with Barker weighing up retaining the same system.
He added: ‘Not that many teams at this level are playing 4-4-2 at the moment which suggests others have the same issue as we do.
‘If you can find somebody who can play in a midfield two they are worth their weight in gold – as are two really good strikers.
‘But we are not a million miles away and will get there in the end.’