The 74-year-old former world heavyweight champion has been hospitalized in a US hospital with a respiratory ailment. An unnamed source has said his condition is "extraordinarily grave."
Ali's spokesman Bob Gunnell said on Friday that the legendary boxer remained in fair condition at a hospital in Arizona for a second day, but media reports say he is gravely ill. A source close to the family told news agency Reuters that Ali was close to death.
The unnamed source said of Ali's condition: "It's extraordinarily grave. It's a matter of hours."
Known globally not only for his prowess inside the boxing ring, Ali is also doubly famous for his civil rights activism. And in December, Ali - who converted to Islam more than 50 years ago - issued a statement rebuking US candidate Donald Trump's call for a ban on Muslims entering the United States.
A 20th century icon in and out of the boxing ring
Muhammad Ali, known globally not only for his storied ring career but also for his civil rights activism, has been hospitalized multiple times in recent years
Ali's last public appearance was in April at the "Celebrity Fight Night" gala in Arizona, a charity that benefits sufferers of Parkinson's disease, of which Ali was diagnosed three years after his retirement in 1981 with a record of 56 wins, 37 by knockout, and five losses.
Fellow boxers like Sugar Ray Leonard have paid tribute, as reports of his worsening condition reverberate around the boxing world.
The Louisville, Kentucky-born boxer's fighting career spanned from 1960 to 1981. He dazzled fans with unparalleled fighting ability in the ring but also his wit and engaging persona outside it.
Ali's opposition to the Vietnam War made him a polarizing figure in the US. He was banned from the sport for years, but the US Supreme Court overturned his conviction for refusing to register for the military draft in 1971.
His conversion to Islam was controversial as was his outspoken stance on civil rights issues. But he lit the Olympic torch in 1996 in Atlanta and was named a UN messenger of peace in 1998. In 2005, he received the Otto Hahn Peace Medal in Berlin. That same year he received the highest US civilian honor, the Presidential Medal of Freedom, from President George W. Bush.
jar/jr (Reuters, AFP)