Blues administrator Andrew Andronikou is adamant Pompey will not be budging on their valuation.
He told The News: "Athens are making noises and I have been in direct contact with them.
"They know our position and they know they have to write a cheque. Unfortunately that has not happened yet. We are waiting for them to come back with something sensible. So far, they have come up with nothing that is suitable.
"There is interest in Diop elsewhere and we want a fee for him. We are not letting him go on the cheap. It is now up to them to meet our valuation. Diop is available for 1m Euros and if they want him they will have to pay that amount.
"We have absolutely no intention of giving him away. If they don't want to pay the fee we want then I know there are others also looking at him.
"I hope they take that into consideration."