The 30-year-old have handed in a transfer request - and it has been accepted.
Lewis was linked with a move away this summer but signed on again for the new campaign.
Chief executive Bill Williams told the club's official website: "It came as somewhat of a shock when Stuart asked to leave as he is held in such high regard by management, players and supporters alike.
“Harry and I had a lengthy discussion with him and came to the conclusion that it was in the best interests of both parties to grant his wish to move on.”