Muhammad Ali retired from boxing in 1981
Muhammad Ali is still in hospital two days after being admitted with a respiratory issue.
There has been no official update on Ali's condition and concern has grown throughout Friday.
Nesta Carter (second from left) and Usain Bolt (second from right) won gold for Jamaica in Beijing
Jamaica's Usain Bolt could lose one of the three gold medals he won at the 2008 Beijing Olympics.
Reuters report that the 'A' sample of one of his team-mates in the 4x100m, Nesta Carter, was found to contain the banned substance Methylhexanamine.
Boxing great Muhammad Ali is being treated in a hospital for a respiratory issue, a spokesman for the former world heavyweight champion has confirmed.
Ali, 74, is being treated by doctors as a precaution and is described as being in a "fair condition". A brief hospital stay is expected.
The Rio Games begin on 5 August and run until 21 August
Up to 31 athletes from six sports could be banned from competing at the Rio Games, Olympic chiefs have said.
The announcement comes after the International Olympic Committee (IOC) retested 454 selected doping samples from the 2008 Games in Beijing.
Saul 'Canelo' Alvarez knocked out Britain's Amir Khan in the sixth round in Las Vegas to retain his WBC middleweight title.
Until the brutal ending, Khan had used his superior speed and movement to frustrate the champion and appeared to be well ahead on points.
