Muhammad Ali is being treated in hospital for a respiratory condition, his spokesman has confirmed to Press Association Sport.
The 74-year-old former world heavyweight champion is being treated by doctors as a precaution, and a brief hospital stay is expected.
Ali, who suffers from Parkinson's Disease, was last admitted to hospital in January 2015 with a severe urinary tract infection.
Bob Gunnell, Ali's media representative, declined to say where the American is being treated.
Ali, who retired from the ring in 1981, is widely considered to be one of the greatest heavyweights in boxing history.
