Jason Cummings moved to Peterborough on loan from Nottingham Forest earlier this summer, and is the likely replacement for Derby bound Marriott.
But the pair seem to get on well despite their short time together, with Cummings posting the following message to Marriott on Thursday:
A fee for Marriott was not disclosed by either Peterborough or Derby, although according to Posh chairman Darragh MacAnthony it is 'miles away' from some of the figures being quoted by the media on Wednesday.
Marriott was strongly linked with a move to Nottingham Forest earlier this summer, but the Reds have signed Lewis Grabban and Hilal Soudani instead.
The 24-year-old scored 33 goals for Peterborough last season - his first full campaign above the fourth tier.
Will the new Derby recruit make Nottingham Forest regret not signing him?