Muhammad Ali's family is at his bedside in a Phoenix hospital and two sources close to the legendary former heavyweight champion told the Los Angeles Times that the situation is "very grave."Ali, who's suffered from Parkinson's disease for more than 20 years, was hospitalized Thursday with a respiratory illness. He reportedly was placed on life support Friday.The boxing officials close to Ali and in contact with his family spoke on condition of anonymity out of respect to the three-time heavyweight champion and sports icon.One of the officials said Ali's condition has deteriorated to the point that an individual close to the situation has said "it could be hours" before his passing.Ali's longtime Parkinson's doctor declined comment when reached by the Associated Press Thursday night.

"I can't really say much more than what's in the papers," said Dr. Abraham Lieberman of the Barrow Neurological Institute in Phoenix.

Several of Ali's daughters reportedly flew to Phoenix late Thursday and early Friday to be with their father.



Laila Ali, herself a former boxing champion, posted a picture Friday afternoon on Facebook of her father holding her daughter when she was an infant.



"I love this photo of my father and my daughter Sydney when she was a baby!" she wrote. "Thanks for all the love and well wishes. I feel your love and appreciate it!!"

Ali has been hospitalized several times in recent years, most recently in early 2015 when he was treated for a severe urinary tract infection initially diagnosed as pneumonia.

Ali has looked increasingly frail in public appearances, including April 9 when he wore sunglasses and was hunched over at the annual Celebrity Fight Night dinner in Phoenix, which raises funds for treatment of Parkinson's.

His last formal public appearance before that was in October when he appeared at the Sports Illustrated Tribute to Muhammad Ali at The Muhammad Ali Center in his hometown of Louisville, Kentucky, along with former opponents George Foreman and Larry Holmes.

Ali has suffered from Parkinson's for three decades, most famously trembling badly while lighting the Olympic torch in 1996 in Atlanta. Despite the disease he kept up a busy appearance schedule until recently, though he has not spoken in public for years.

Doctors say the Parkinson's likely was caused by the thousands of punches Ali took during a career in which he traveled the world for big fights.

An iconic figure who at one point was perhaps the most recognized person in the world, Ali has lived quietly in the Phoenix area with his fourth wife, Lonnie, whom he married in 1986.

News of his hospitalization brought well wishes from boxers and others on Twitter, including Sugar Ray Leonard, who modeled his career after Ali's.

"Prayers & blessings to my idol, my friend, & without question, the Greatest of All Time @MuhammadAli ! #GOAT," Leonard wrote.

The Associated Press contributed to this report