A well-informed source tells NBC News that Muhammad Ali is in "grave condition" in a Phoenix-area hospital.
The 74-year-old former heavyweight champion's family gathered by his bedside just a day after Ali spokesman Bob Gunnell said Ali was hospitalized in what was to be a brief stay.
Ali has been dealing with advanced Parkinson's disease in recent years — an illness that experts say can lead to complications and can affect patients' breathing. He was previously hospitalized in December 2014 and January 2015 for a severe urinary tract infection.
He has been on the national stage in recent months, calling for more understanding after Donald Trump suggested banning all Muslims from entering the U.S.