They have also made it clear players must still be sold or accept lower wages, or the club will close down.
In June, Portpin agreed to complete its purchase of the club on condition the wage bill was reduced through player sales and compromise agreements.
But administrator Trevor Birch has so far been unable to achieve sufficient savings by this strategy alone.
"Under the terms of the Company Voluntary Arrangement that was agreed with creditors, Portpin agreed to complete its purchase of the club on the condition that the wage bill was reduced through player sales and compromise agreements," said Birch.
Portsmouth cannot afford to keep any of their eight contracted players - Tal Ben Haim, Greg Halford, Erik Huseklepp, Dave Kitson, Liam Lawrence, David Norris, Luke Varney, Kanu
"We have made progress in this respect over the past few weeks but there is still more that needs to be done if the club is to meet the pre-conditions for Portpin's purchase."
In February, Pompey made around 30 staff redundant including chief executive David Lampitt and the club face liquidation if they cannot reduce their playing staff further.
In total they have eight senior players left on the books and most of them will have to leave for the club to survive.
Those players are Tal Ben Haim, Greg Halford, Erik Huseklepp, Dave Kitson, Liam Lawrence, David Norris, Luke Varney and Kanu.
"Time is running out and, unless I can see a greater probability of player sales and compromises being completed in the near-term, the purchase will not go ahead and the club will have to close," added Birch.
"We have spoken to all of the club's staff and players and started a redundancy consultation period.
"I sincerely hope that we can complete the sale of the club and avoid the need for redundancies - and I will continue to do all I can to safeguard the future of the club - but I believe that staff need to be aware of the situation so that they have as much of an opportunity as possible to explore other options.
"This has been an incredibly difficult time for the staff, many of whom have loyally served the club for a number of years, and I recognise that it is extremely upsetting for them.
"This announcement is not in any way a reflection on them - in fact, I'm sure that we would not have got this far without their support."
According to the local paper -The Portsmouth News, Administrator Trevor Birch has told a delegation of Pompey fans the club is two weeks from going out of business. Members of the Pompey SOS group had gone to the Blues’ training ground this morning to hand letters to the players pleading with them to waive their wages.
Four of the five players accepted the letter. However. Pompey’s highest wage earner, Tal Ben Haim, refused the letter.
The stumbling block is that the players involved are on such high wages potential suitors can't get anywhere near their currnet wage levels.