Long-serving defender Kallum Griffiths, who has been with the club since 2009, has opted not to sign an improved offer from the club.
Griffiths has racked up 389 appearances for Moors, scoring 19 goals during his nine-year stint.
The full-back has won the Northern League Division One title on four occasions in 2010, 2011, 2012 and 2014, the Durham Challenge Cup in 2012, the JR Cleator Cup in 2011, 2012, 2013, 2014 and the Northern League Cup and FA Vase in 2013.
Griffiths was named Supporters Player of the Season for the 2016/17 Evo-Stik Northern Premier Division promotion winning campaign.
After choosing not to extend his stay, Griffiths said: “Leaving a club I have spent so long at was a very difficult decision, and one I have thought about long and hard for a while now.
“I love the club and have spent nine brilliant years here, but it’s now time for me to move on and pursue my next challenge.
“I would like to thank the fans, players and everyone associated with Spennymoor Town Football Club who have made my experience one which I will never forget.”
Moors boss Jason Ainsley was full of praise for Griffiths after he announced his departure: “He has been with myself and the chairman for so long he has been part of the family.
“Unfortunately, Kallum has decided he wishes to pursue other opportunities, but I know he leaves the club with a heavy heart. He has been an outstanding servant for this football club.”