Derbyshire have allowed batsman Paul Borrington to leave the county but have offered Greg Cork a new two-year contract.
Borrington, 26, had made over 2,000 runs in his 49 first-class matches with the county, making nine fifties and two centuries since making his debut in September 2005.
However, his failure to be offered a new contract has prompted him to leave Derbyshire with immediate effect.
Derbyshire's elite performance director Graeme Welch said: "Paul has been with the club for a long time and is a popular player among the lads, so it's sad to see him go.
"However, we have to move on and I speak for everyone at the club when I wish the lad all the very best for the future."
But left-arm seamer Greg Cork, son of Sky Sports Cricket pundit Dominic, has been offered new terms to stay on.
Cork, 19, has been a regular in the second XI set-up and made six appearances in this year's NatWest t20 Blast, taking six wickets.
Welch added: "We've thrown him in at the deep end in Twenty20 cricket this summer and his performances have been improving with each game.
"If he continues to work hard at his game, listens and continues learning his trade, there's potential there for a really bright future."