Former actor Joaquin Phoenix is not suffering from a mental illness, his publicist has said.

Susan Patricola said claims by a US doctor that there was “something wrong” with Phoenix, who recently launched a rap career, were “astonishingly inappropriate”.

"How absolutely inappropriate for a doctor who has no personal interaction or relationship with someone to diagnose them. And to do so in a public forum," Patricola told E! News.

Chicago psychiatrist Paul Dobransky commented on Phoenix in an article in the Los Angeles Times newspaper last week.

He said the former actor had displayed “socially inappropriate behaviour” during a recent appearance on the Late Show with David Letterman”, where Phoenix at times appeared disinterested.

Dobransky also criticised actor Ben Stiller's decision to mock Phoenix onstage at the Academy Awards in February.

"There is something wrong. And it's beyond drug abuse,” the psychiatrist said.

“I was pretty offended by that [Ben Stiller] skit at the Oscars. It struck me as potentially beating down on the mentally ill."

Phoenix's sudden transformation from acclaimed actor into rapper has been widely scrutinised by the media – and prompted speculation that it is part of a hoax.

Internet footage from his debut gig in Las Vegas earlier this year shows Phoenix rapping incoherently and falling from the stage.

In a recent interview, Phoenix insisted that his ambition to launch a hip-hop career was genuine, and that music, not acting, “will be the dominant theme in my life." 

Joaquin Phoenix