U.S. boxing great Muhammad Ali poses during the Crystal Award ceremony at the World Economic Forum (WEF) in Davos, Switzerland January 28, 2006. [Photo/Agencies]

Former world heavyweight champion Muhammad Ali was close to death in a Phoenix-area hospital on Friday, Reuters quoted a source close to the family as saying.

Ali, 74, one of the world's most celebrated athletes, was hospitalized this week for a respiratory ailment. The family spokesman has said he was in fair condition, but speculation has swirled about his health.

Asked about Ali's condition, the source said: "It's extraordinarily grave. It's a matter of hours."

The source said he had spoken with Ali's wife, Lonnie. "It could be more than a couple of hours, but it's not going to be much more. Funeral arrangements are already being made."

The spokesman, Bob Gunnell, has not responded to repeated requests for comment about his condition.

Ali has suffered from Parkinson's disease for more than three decades and has kept a low profile in recent years.

The New York Post and the International Business Times cited a report on the Radar Online website as saying Ali had been placed on life support. The source could not comment on that report.

Ali's last public appearance was in April at the "Celebrity Fight Night" gala in Arizona, a charity that benefits the Muhammad Ali Parkinson Center.

At the height of his career, Ali was known for his dancing feet and quick fists and his ability, as he put it, to float like a butterfly and sting like a bee.

Nicknamed "The Greatest," he retired from boxing in 1981 with a 56-5 record. Ali's diagnosis of Parkinson's came about three years after he retired.

Ali, born in Louisville, Kentucky, as Cassius Marcellus Clay Jr., changed his name in 1964 after his conversion to Islam.

Ali's daughter Laila, a former boxer, tweeted a photo of her father kissing her own daughter, Sydney. She thanked supporters for their wishes for Ali, saying, "I feel your love and appreciate it!"