Guy Whittingham admitted he and his players had let Pompey fans down and vowed: It will never happen again.
And he has moved swiftly to guard against a repeat with Therry Racon set to train with the Blues today.
Pompey were embarrassed 4-2 at York on Saturday – a result which demolished their unbeaten League Two away record.
It was a wretched performance from the visitors, with a wonder goal from Jed Wallace the sole positive in a Bootham Crescent debacle.
Comfortably the worst display of the season so far, Pompey were always second-best against a bright and hard-working Minstermen outfit who collected only their second league win.
For Whittingham, it was a humbling that was hard to stomach, particularly in front of 1,357 away fans who made the arduous trek to Yorkshire.
There will be changes to his starting line-up for the visit of Rochdale this weekend, while free agent Racon is expected from France today with the possibility of rejoining.
And the boss has promised there will not be a repeat of the York display.
He said: ‘You cannot stand by and think “we will put that same side out again and hopefully turn it around”.
‘You have got to think very clearly about why it happened and try to make sense of it.
‘We have got to make sure the players taking their place next week – whoever they may be – know that number one is work-rate.
‘Jed is the only one who can come away from that with any sense of having done work.
‘I don’t think we will see it again, I really don’t because we have all let people down.
‘It’s not a case of singling out people. Fans travelled all that way and all they want to see is people give 100 per cent, and that is from everybody – myself, the staff and the players.
‘We have to make sure that doesn’t happen again.
‘You have got to hope that pride kicks in. We worked very hard this summer to get some good players and we believe they are good players.
‘I believe that was a one-off – I don’t think we will see a Portsmouth side as lacklustre as that again.’
Pompey were 1-0 down at the break after Wes Fletcher netted when John Sullivan failed to hold a free-kick.
That scoreline flattered the visitors after an abject opening 45 minutes but it only got worse as the second half developed.
Whittingham added: ‘At half-time I told them “listen, you cannot just come to a team like York – you have got to go out there and play, there is nothing else without hard work”.
‘Voices weren’t raised, it was just a reminder about what they needed to do and I think at the start of the second half we did that, we were a lot better.
‘Jed’s scored his goal and you think you are back in it – then we conceded again and dropped off and went back to where we were.’