Llewellyn looks certain to continue playing

"We are in a process which amounts to a redefining of the squad," said Ospreys joint managing director Roger Blyth.

The Ospreys say Llewellyn, who has been named in Wales' Six Nations squad, is being allowed to "explore new career opportunities".

The departure of Llewellyn and Thomas follows the decision of Ospreys skipper Scott Gibbs to retire mid-season.

Llewellyn is Wales' most capped forward with 83 caps, seven of which were earned as captain of the Welsh team.

Thomas joined the Ospreys from Bath last summer

He played over 300 games for Neath before joining the Ospreys and captained the Welsh All Blacks for a record seven seasons from his debut at the club as a 19-year-old in the 1988/89 season.

"Gareth has been an exceptional servant of Welsh rugby throughout his career, which has seen him receive more Welsh caps than any other second row.," said Mike Cuddy, the other Ospreys joint managing director.

"We are grateful to him for his effort not only at the Ospreys but for his tremendous input at Neath RFC before that, where he captained the team over so many seasons.

"I know everyone at the Ospreys and supporters old and new will throw their weight behind Gareth as he considers the direction he now wishes his career to take."

Blyth added: "The full weight of the Ospreys management team and board will be behind (coach) Lyn Jones as the necessary changes are now made to keep the team moving forwards."