The South Africa international is expected to join Portsmouth in January.
And Allardyce said: "There is a price to be met if someone wants to buy Benni McCarthy.
"If the club is happy with that price we will go to Benni and say we've accepted a deal from a certain club. Now it's up to you to see if you can sort your side of it out.
"But we would have to have a replacement for him to allow it develop in to him being transferred."