"Chris is now going to move on," boss Gordon Strachan said.
"He wants to change his whole lift in terms of life, the club and the area he lives in. He's got great experience and he's had a rough time with injuries."
Strachan added: "He understands that he needs to go and play regularly and he has decided to move to a different area and continue his career somewhere else.
"I hope the kid gets over his injuries and starts to enjoy his football because he's got plenty left in him."
Riggott made just seven appearances for the club this season, having completed a total of 148 appearances, scoring eight times.
During his career at the Riverside the defender had been involved in the League Cup triumph against Bolton at Wembley, the Uefa Cup final loss to Sevilla in Eindhoven and top-flight football under former bosses Steve McClaren and Gareth Southgate.
Source: BBC Sport
Source: BBC Sport