Guy Whittingham revealed Pompey’s latest defensive aberration has left him unsure of his best back four.
The Blues boss criticised his side’s defending after Saturday’s 2-1 defeat to Scunthorpe made it four successive defeats.
In contrast, he was satisfied with his team’s work on the ball and their attacking capabilities.
Against the Iron, loan recruit Dan Potts was granted a debut at left-back with Joe Devera switching to right-back to replace Danny East.
That left Sonny Bradley and Bondz N’Gala to continue their regular partnership at the heart of the defence.
Regardless, Pompey’s tally rose to 35 goals conceded in 21 games in all competitions so far this season, with only four clean sheets.
And having witnessed his side concede a poor goal to David Syers in each half at Fratton Park, Whittingham admitted he was now at a loss to name his most effective back line.
He said: ‘Do I know my best back four? Probably not.
‘You asked me four weeks ago and I said “yes” and that’s where we are.
‘But with a youngish back four, confidence can go quite quickly.
‘We wanted to get that experienced one and couldn’t find one in the summer.
‘We could criticise people here, there and everywhere but we don’t defend our goal well enough – end of story.
‘In the last few games sometimes you look and it is individual errors costing us.
‘On Saturday it wasn’t so much individual errors, it was more the organisation wasn’t as good as we hoped it would be. So that is what we have got to get right.
‘With any set-play when somebody scores, if you have got man-to-man markers and they are free then there is somebody at fault.
‘I felt for the first goal we could have got something on it when the ball was delivered and for the second one we didn’t get ourselves in the right position.
‘They have put a lot of people in there and I think Trevor (Carson) was blocked so he couldn’t get out to it. You just expect somebody to get something on it.
‘You look at the other end and the chances that came into their box.
‘It’s not always by luck they get a block in or it falls to them, that is what we have got to make sure we tighten up on.’
Pompey have now used nine different players in defensive positions this season.
No fewer than four of those were on the bench against Scunthorpe, with East introduced for Devera in the 78th minute.
Whittingham added: ‘It has been a little bit forced on us in a way with the injuries we had and suspensions.
‘Obviously finding that settled back four is what you want to do.
‘Where we did well last year was we had the spine of the team that did really well – two centre halves, two central midfield and two centre forwards that we could keep.
‘We are keeping the two centre-halves together, Simon Ferry has done well and Johnny (Ertl) had a decent game again Saturday.
‘I don’t think the effort is lacking, that is one thing I definitely don’t think.
‘It’s just not coming together for us at the moment.’