PHOENIX -- Boxing great Muhammad Ali is hospitalized in the Phoenix area with what two people familiar with his condition say may be more serious problems than his previous hospital stays.
The people told The Associated Press on Thursday that Ali is fighting respiratory issues that are complicated by the Parkinson's that he was diagnosed with in the 1980s. The two spoke separately in describing Ali's condition that they say is concerning to family members.
The sources declined to be identified because they were not speaking on behalf of the family.
A spokesman for Ali sent out a release earlier Thursday saying the former heavyweight champion is being treated at an unidentified hospital for a respiratory issue. Spokesman Bob Gunnell said that the 74-year-old was in fair condition, and that a brief hospital stay was expected.
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 in recent years, including on 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 communicated verbally in public for years.
Doctors say the Parkinson's was likely caused by the thousands of punches Ali took during his career, where he traveled the world meeting opponents in big fights.
An iconic figure who was at one point arguably the most recognized person in the world, Ali has lived quietly in the Phoenix area with his fourth wife, Lonnie, who he married in 1986.
Lonnie Ali spoke with CBS affiliate KPHO last month about her husband's battle with Parkinson's.
"Someone like Muhammad who has done everything and who has lived life to the fullest... having a disease like this that makes you sit down and take account of your life. You're not as active," she explained.
She went on that she wanted the community to know that Ali "is somebody who never feels sorry for himself. He's not one who says 'why me?' He's a real champion. I learn every day from this man: the courage, the strength and the grace that he lives with his illness. For most people, it would put them in bed and put covers over them. They would give up. He does not stop. He continues to live life and that's very important."
News of Ali's hospitalization brought well wishes from boxers and others on Twitter, including Sugar Ray Leonard, who modeled his career after Ali.
Born Cassius Clay in 1942, Muhammad Ali became an Olympic gold medalist in 1960 and the world heavyweight boxing champion in 1964. Following his suspension for refusing military service, Ali reclaimed the heavyweight title two more times during the 1970s.
Ali retired from boxing in 1981 and devoted himself to social causes. He traveled the world on humanitarian missions, mingling with the masses and rubbing elbows with world leaders. Ali received the Presidential Medal of Freedom from President George W. Bush in 2005.
The Muhammad Ali Center, in Louisville, is dedicated to Ali's humanitarian causes and also showcases his boxing career.
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