Peterborough chairman Darragh MacAnthony says Jack Marriott has had his "head turned" by Frank Lampard's Derby, but they must improve on the three bids they have submitted.
Marriott, 23, scored 27 League One goals last season.
"He's told me the figures that have been mentioned and it's life-changing compared to what he's on. Of course he wants to go," MacAnthony said.
"We will sell a player, we always have done - we never stand in anyone's way."
Steve Evans' side have already signed 14 players this summer, with the same number leaving London Road since the end of last season.
MacAnthony told the Posh website: "Jack's head's been turned in a big way.
"If they (Derby) want to back their manager and buy him they know what they've got to do, but I certainly won't be letting him go for where they are at the moment, not a chance."
He confirmed Marriott is also keen on a move to another unnamed club, who have also shown interest in him.
A trio of players have joined Derby this week, with Florian Jozefzoon, Mason Mount and Harry Wilson the first players to sign for the new Rams boss.
And ex-England midfielder Lampard is eager for Marriott to become his fourth new signing since taking over.
"There is no movement from what the owner has said, but we will see," Lampard told BBC Derby Sport.
"Jack is a good player," Lampard added. "Anyone who is aware of Peterborough and Jack Marriott in League One last year will know the prolific amount of goals he scored."