"Newcastle United can confirm that Joey Barton has been placed on the transfer list," the club said on its website.
"The player has been advised that he can leave the club on a free transfer."
Barton, 28, has flourished at Newcastle who stood by him when he was jailed for assault in 2008 and was then given a suspended four-month sentence for attacking team-mate Ousmane Dabo while at Manchester City.
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