Pompey are working on a one-in, one out transfer policy.
Kenny Jackett will have to sell players before he adds any further new faces to his squad this summer.
Yesterday’s addition of Sean Raggett takes the Blues squad to 24 players - an optimum number in Jackett’s view.
Pompey are still on the lookout for new faces this summer, but after bringing in Raggett, James Bolton, Paul Downing, Ellis Harrison and Ryan Williams there will need to be a departure first.
Jackett said: ‘We’ve got a good balance in terms of our squad. We won’t be going over that.
‘I’d suggest that if we bring people in, there will be people going out before that.
‘So, in terms of numbers, the five signings have brought us up to what I like to be.
‘That’s two players for every position with three senior keepers at present, if we count Durnin as a youth-team keeper.
‘We’re without Jack Whatmough for the first half of the season, so quite obviously we’re planning without him.
‘Jack aside takes us down to 23 - and that’s almost ultimate numbers.’
Jackett added he’s confident he’s signed players this summer who are coming into their best years as they arrive at Fratton Park.
And that leaves them in a good place to make an immediate impact at their new club.
He added: ‘There’s a lot to consider in terms of progressive signings and players who are coming into their best years.
‘If we’re looking, James Bolton is 24, Ryan Williams is 25, Raggett is 26 and we’re just getting them at their peak. That’s the aim.
‘There are big targets for them coming to a clubs like this and exciting times ahead for them as well as a big challenge. That’s a really good situation.
‘In terms of buying players you want future and immediate.
‘It’s no good buying players for three years’ time - it’s what they do in that time and they have to play to progress.
‘Matt Clarke is a good example of that. He left Ipswich as a very young man and got to 150 games at 22. That base of experience has helped him.
‘So we want that balance of now and the future - but most importantly it’s the standard of the player. You have to get that right.
‘That’s the big call and decision - and what I have to feel makes a difference.’