Boxing legend Muhammad Ali is so ill from Parkinson's disease that he can now barely talk.

Ali's brother, Rahman, revealed the health update as the former world heavyweight champion failed to attend the premier of his bio-pic I Am Ali in Hollywood.

Ali, 72, whose tongue was even quicker than his lightning fists in helping him dominate the sport, was diagnosed with the disease in 1984.

"I have not been able to talk to my brother about this because he is sick," Rahman told The Sunday People as questions were raised about Ali's absence from the premier of a movie he was also to ill to help with in production terms.

"He doesn't speak too well. But he is proud that we are here for him. He has given this film his blessing".

The family is planning a private screening for Ali at his Arizona home.

The Times said the documentary film directed by Clare Lewins, revealed an intimate portrait of the boxer's life, told through a series of oral histories with Ali's family and rivals including Mike Tyson and George Foreman.

The feature-length also used Ali's personal archive of audio journals.

His son, Ali Jr, said in January he believed there was "no chance" his father would survive until the end of 2014.

"I just want, hope and pray to God that this awful disease takes my dad sooner rather than later," he said.