Fry had previously stated how Forest were the club that Marriott favoured joining this summer, due to their illustrious history.
But, having met with Frank Lampard, Fry now thinks that Derby are leading the race for the clinical forward.
“Jack does want to join Nottingham Forest,” Fry admitted. “But Derby’s interest is recent and I would say they have a better chance of making us the right sort of offer.
“I spoke to Frank Lampard and his father at the play-off finals which was before he had got the Derby job, although it was common knowledge he would be appointed."
Posh are said to be looking for £6.5 million for Marriott, which means he would be an expensive addition for either Derby or Forest to make.
Marriott was the top scorer in the Football League last term, when he netted 33 goals for Posh.
The former Luton man looks ready to make the step up to the Championship, with eight teams believed to be chasing his signature.
Forest appear to have money to spend this summer, with Aitor Karanka already looking to bring in Joao Carvalho for £13 million.
Derby don’t have such considerable funds, but could raise money for Marriott from the sale of Matej Vydra.