Ali,72, has had Parkinson’s disease since 1984 and there have been rumours his health is deteriorating.
“I don’t know that he is more or less at risk than anyone else but anything can happen,” Dr. Abraham Lieberman told BBC Radio 5 live’s Sportsweek.
“I don’t see anything immediately that leads me to think that he is going to die in six months or a year.”
Lieberman added: “People do not die of Parkinson’s. They develop trouble swallowing, they develop pneumonia, fall and bang their heads. His family take extraordinary care of him.”
Ali appeared frail when he attended the opening ceremony of London 2012 Olympics and, according to Lieberman, struggles to walk.
“He is in good spirits,” added Lieberman, who is also the director of the Muhammad Ali Parkinson Centre.
“He has some trouble walking but, overall, for someone who has had Parkinson’s for 30 years he is doing OK.”