The boxing great was recently admitted to a Phoenix-area hospital with severe respiratory problems. At the time, his spokesperson told reporters the hospital stay was expected to be brief.
But on Friday, several outlets said Ali's family had been called to his bedside as his condition continued to deteriorate. The Daily Mail reports Ali has been placed on life support.
The three-time heavyweight champion is a legendary figure both inside and out of the ring. Ali is known both for his famous bouts with Joe Frazier and Sonny Liston, and for being stripped of his boxing license over his refusal to be drafted for the Vietnam War.