Derby County have told out-of-contract striker Chris Martin the "door is open" for a return, despite him failing to agree terms on a new contract.

Martin, 31, who has scored 76 goals in 226 games for the Rams, had agreed a short-term extension to see out the existing Championship season.

However, he and representatives were unable to negotiate an agreement beyond the 31 July expiry of his current deal.

"He has made a telling contribution," chief executive Stephen Pearce said.

"We wish to thank Chris for his seven-year service to the football club.

"And we will endeavour to remain in dialogue with him and his representatives and will always leave the door open for a potential return if he does not find a suitable club."

Martin has had a mixed history with Derby, having previously been sent on loan to Fulham, Reading and Hull while not part of the Rams' first-team picture.

His most successful season at Pride Park came in 2013-14, when as top goalscorer he guided the club to the Championship play-off final, where defeat by QPR ended their Premier League hopes.

Meanwhile, 19-year-old defender Lee Buchanan has extended his contract with the Rams until 2022 after making seven appearances during the 2019-20 campaign.