Sources have confirmed to Scripps affiliate ABC15 that a Phoenix-area fire department responded to Muhammad Ali's Phoenix-area home on Tuesday.
The Associated Press reported this morning that the 74-year-old former boxing champion's hospitalization may be more serious than his previous trips to the hospital.
A spokesman said Ali was being treated for a respiratory issue and was expected to only spend a short time in the hospital.
Ali, who made an appearance in April at Celebrity Fight Night in Phoenix, was diagnosed with Parkinson's in the 1980s.
Ali racked up 56 victories in his 21-year professional boxing career, including an Olympic gold medal and became the first fighter to capture the heavyweight title three times.