Muhammad Ali in hospital

Former world heavyweight boxing champion Muhammad Ali has been hospitalized for a respiratory issue, family spokesman Bob Gunnell said on Thursday.

Gunnell said in a statement that Ali was in fair condition but that a brief hospital stay was expected.

Ali, 74, has been suffering from Parkinson's disease for more than three decades and has kept a low profile in recent years. His last public appearance was in April at the 'Celebrity Fight Night' gala in Arizona, a charity that benefits the Muhammad Ali Parkinson Center.

At the height of his career, Ali was known for his dancing feet and quick fists and his ability, as he put it, to float like a butterfly and sting like a bee.

Ali, who lives in Phoenix, Arizona, has suffered health problems in recent years and was admitted to hospital in December 2014 with what was believed to be a mild case of pneumonia.

Doctors later determined he had suffered a severe urinary tract infection, for which he received further treatment in January 2015.