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.
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.
Doctors say the Parkinson's was likely caused by the thousands of punches Ali took during his career, where he travelled 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.
"Prayers & blessings to my idol, my friend, & without question, the Greatest of All Time @MuhammadAli ! #GOAT," Leonard wrote.
