Forward Jose Baxter, who was suspended twice in nine months, is among 10 players released by Sheffield United.
Baxter, 24, played the last of his 93 league games for United in February, with the ex-Everton trainee then banned for an unspecified reason by the club.
In July 2015 he was suspended by the Football Association for failing an out-of-competition drugs test.
Midfielder Ryan Flynn, 24, who scored 13 goals in 153 league games, has also been released.
Meanwhile, Dean Hammond, who made 34 Blades appearances during his loan spell from Leicester City in the 2015-16 season, has activated a clause in his contract to remain at Bramall Lane on a permanent deal.
However, the 33-year-old has immediately been placed on the transfer list alongside Kieron Freeman, Kieran Wallace, James Wallace, Paul Coutts, Martyn Woolford and Diego De Girolamo.
Goalkeeper George Long has been offered a new deal while Alex Baptiste, David Edgar and Conor Sammon have left the club after their loan deals expired.
Mark Howard, Bob Harris, Callum McFadzean, Terry Kennedy, Harrison McGahey, Jay McEveley, Florent Cuvelier and Jamal Campbell-Ryce have all been released.