Muhammad Ali is being treated in a hospital for a respiratory issue, according to a spokesman for the legendary heavyweight boxer. Ali is 74, and was diagnosed with Parkinson's disease in 1984.

The spokesman, Bob Gunnell, told the Associated Press that Ali is in fair condition and is being treated as a precaution. Gunnell did not specify where Ali was being treated or when he was admitted, but did say in a statement that "a brief hospital stay is expected."

Ali was hospitalized in January 2015 with a urinary tract infection after being found unresponsive at his home in Scottsdale, Arizona. In December 2014, he was treated at a hospital for pneumonia.

In recent years, Ali has kept a relatively low profile, compared to his younger years, when the brash pugilist was renowned for belittling his opponents and taking controversial political stances. He last fought in 1981, losing a unanimous decision to Trevor Berbick, a year after getting pummeled by Larry Holmes at a time when many pleaded with him to retire.

Before the end of his career, though, Ali carved out a place in boxing lore as the self-described "greatest of all-time," a title with which plenty of fans and analysts agree. Beginning his pro career in 1960, the Louisville native first won the heavyweight title in 1964, in a stunning upset of Sonny Liston.

Stripped of his title in 1967 for his refusal to enter the draft for the Vietnam War, Ali would not fight again until 1970. He suffered his first loss in 1971, in the first of three epic battles against Joe Frazier, before regaining his title in 1974's "Rumble in the Jungle" against George Foreman.

All told, Ali finished with a record of 56-5, including 37 wins by knockout. In 1996, he created an indelible image by lighting the stadium cauldron with the Olympic flame at the Summer Games in Atlanta, and in 2005, he received the Presidential Medal of Freedom from George W. Bush.