Hull have released former Great Britain centre Martin Gleeson and opted not to give second-rower Mike Burnett a new contract.
Gleeson, 31, joined Hull on an 18-month deal in April after being released by Wigan, but he made only seven appearances and has been on sick leave since June due to a stress-related illness.
"Hull FC have terminated the contract of Martin Gleeson," said chief executive James Rule. "We thank him for his contribution to the club and wish him the best of luck in the future."
Hull, who on Thursday signed Bradford prop Andy Lynch on a two-year deal, are also parting company with Burnett, who spent the entire 2011 season on loan at Harlequins, and promising academy player Luke Briscoe, younger brother of England international Tom.
Briscoe, who joined the club as a 15-year-old and has impressed in the Under-18s and Under-20s teams, was offered a new contract but Hull say they have lost his services to Leeds.
"The club is extremely disappointed to announce that Luke Briscoe is leaving Hull FC to join Leeds Rhinos," said Rule.
"The entire youth and academy structure will undergo a full review with the clear objective of preventing this ever happening again."