Ali, 74, is being treated for a respiratory issue at a hospital in Phoenix, where he lives, family spokesman Bob Gunnell said in a statement, according to ESPN.
"A brief hospital stay is expected," Gunnell said, adding that he is in fair condition and is being treated by his team of doctors.
The three-time heavyweight champion, who suffers from Parkinson's disease, retired from boxing in 1981.
- AFP