Sullivan believes Newcastle face losing Demba Ba for around half his get-out clause, claimed to be around £7m, because of payments due to the player if he leaves the club.
"I'm told he's got a £7m get-out at Newcastle and he gets half the money over that. They keep denying it but I think you'll see in the summer he will leave Newcastle or he'll get a monstrous rise to stay there," he told the West Ham Till I Die website.
"If they get about four million, half will go to him, so if they sell him for £7m they'll only net about three because they paid his agent £2m to get him out of here. Getting £3m is not bad, but for a player of his quality it's not fantastic."