The News of the World says England Under-21 hitman Campbell has agreed a £6million switch - but he still has a year left on his Old Trafford deal and did not ask for a transfer.
That should entitle him to a loyalty bonus for the remaining 12 months of his contract and Campbell's camp has told United bosses he is prepared to sit tight. He would by rights be able to then talk to prospective buyers in January about a move.
Any buying club would then only face a compensation payment for Campbell.
A source said: "Fraizer wants to go to Hull but didn't ask for a move. The deal needs a sweetener to get it moving. If it doesn't come, Fraizer is prepared to play a waiting game."