Middlesbrough have released eight players who are out of contract this summer, including defenders Frazer Richardson and Stuart Parnaby.
Richardson, 31, made 11 appearances for Boro following his arrival last August but then was sent on loan to Ipswich.
Parnaby, also 31, returned for a second spell in August 2012 and played 21 games, three of which came in 2013-14.
Jayson Leutwiler, Lewis Sirrell, Birger Meling, Jake Fowler, Cameron Park and Matthew Waters also leave the club.
Swiss goalkeeper Leutwiler was limited to five outings for Boro since joining the club from Basel in 2012.
Loanees Nathaniel Chalobah, Danny Graham, Tomas Mejias, Kenneth Omeruo and Jozsef Varga have returned to their respective parent clubs.