Cambridge United centre-back Josh Coulson has been transfer-listed along with four other players.
The 26-year-old, who is the club's longest-serving player and played every minute of every match last season, has one year left on his contract.
Greg Taylor, Johnny Hunt, Robbie Simpson and Jordan Slew have also been made available to other clubs.
Former Manchester United midfielder Luke Chadwick has been released. as has striker Tom Elliott.
Matteo Lanzoni, Mitch Austin, Richard Tait, Michael Nelson, Ian Miller, Ryan Bird and Nathan Arnold, whose contracts are about to expire, have not been offered new deals.
Meanwhile, midfielder Tom Champion has left the U's by mutual consent.