Muhammad Ali's personal doctor has revealed he cannot be sure that boxing contributed to the former heavyweight world champion's Parkinson's Disease.
Ali, considered by many to be the greatest boxer of all time, has suffered with the neurological syndrome since the mid-1980s and it has often been presumed that blows to the head during his 21-year professional career were a contributing factor to his condition.
But Dr Abraham Lieberman, who is the Medical Director of the Muhammad Ali Parkinson Centre, admits that it is not possible to be entirely sure what caused Ali to suffer from Parkinson's.
"It's only over the last 10 years that he's had a lot of trouble walking, with falls," he told BBC Radio Five Live's Sportsweek programme.
"So his course has been more that of typical Parkinson's Disease. If you look at the MRI of his brain it looks pretty good but it's very difficult to factor in what sort of role did boxing play.
"People ask me about this and I tell them: look at George Foreman. He boxed longer than Muhammad did, took many more blows to the head and he's on television selling his cookware.
"I think that he [Ali] has typical Parkinson's Disease. Did the boxing contribute? I don't know. It may have."
"He's in good spirits, he has some trouble walking but overall for having had Parkinson's for 30 years, he's doing okay"
Dr Lieberman gave the impression of a happy retirement for Ali - who was known as Cassius Clay before joining the Nation of Islam and changing his name - and stressed that, despite some reports, there is no reason to fear for his health.
He said: "He's had Parkinson's since about 1984, that's almost 30 years, that's a long time in Parkinson's.
"He's in good spirits, he has some trouble walking but overall for having had Parkinson's for 30 years, he's doing okay."
He added: "Muhammad is now 72 so you can have a heart attack or you can have a stroke.
"I don't know that he's more or less at risk than anyone else but anything can happen to you.
"How do people with Parkinson's Disease die? They don't die of Parkinson's Disease, they develop trouble swallowing and they develop pneumonia and he doesn't have trouble swallowing.
"They fall, they bang their head - his family takes extraordinary care of him.
"I could have a heart attack or a stroke and die but I don't see anything immediately that leads me to think he's going to die in six months or die in a year. I can't say that."