Although he has stopped short of publicly revealing the progress of specific cases out of concern that it could alert rivals and weaken Blues negotiation.
A total of 12 members of Danny Cowley’s squad have deals expiring this summer – plus the departure of their five loan players.
Of those, six are known to possess club options, allowing Pompey to potentially extend their stay by an additional 12 months.
Among the dozen whose deals are up at the season’s end are Marcus Harness, Sean Raggett, Michael Jacobs, Louis Thompson, Aiden O’Brien, Reeco Hackett and Shaun Williams.
Cullen is adamant discussions have already taken place ahead of League One’s final month, but is tight-lipped over player identities.
The Blues’ chief executive told The News: ‘Contracts are a work in progress, we have regular recruitment meetings.
‘I wouldn't want to comment on individual players because this is private, you have to be respectful of individual players and, naturally, those discussions are ongoing.
‘What is important is we look at what we want for next season, in terms of players we need to recruit, those we’d like to retain, and the players we'd be very keen to exercise the options open to us.
‘It is work in progress. It’s about assessment and keeping our business as private and confidential as we can, otherwise then you start to alert other clubs to what you are doing.
‘There will always be speculation, people will always pick things up, that’s the nature of the beast, but we need to do what we can to keep that business going.
‘We are in a position where we’re getting some real clarity on what the squad is starting to look like – and those negotiations and discussions about where the club sees players for next year.
‘It is getting it right and then shaping it within the whole structure of the squad. So there’s debates about that, and debates about what’s an ideal number to have.
‘We are guided by Danny, with lots of other people also involved in the process. It’s very much getting that advice from as many quarters as we possibly can.
‘Fundamentally, those decisions on players - the ones we want to keep and the ones we want to recruit - and whatever structure we have in place, must be what the head coach wants.’
Also out of contract are Callum Johnson, Jayden Reid, Jay Mingi, Ollie Webber and Paul Downing.
Although Cullen will not be putting a deadline for agreements to be reached for any of the dozen nearing the end of their existing deals.
He added: ‘I won’t be held to a date, these things will start to happen.
‘The date you have for an out-of-contract player is already in the regulations, in terms of when they technically become free agents.
‘For players under-24, there's a different scenario, and with those that have options, you are again regulated by the dates.’