Former Springbok rugby player Joost van der Westhuizen is reported to have undergone experimental stem cell treatment for a fatal motor neuron disease (MND).
Van der Westhuizen's neurologist Dr Jody Pearl told The Star that the treatment was safe, but there was no guarantee it would have any real benefit.
"We don't know if we'll be able to help with the MND... (but) therapy is the most promising treatment we have to date in any kind of degenerative condition," she said.
"But I think we need to be cautiously optimistic."
Van der Westhuizen, 40, said he would continue to fight the disease, for which there is no known cure.
"I've been a fighter all my life," Van der Westhuizen told The Times daily.
"I'm going to fight this thing mentally and to the best of my ability.
"Don't worry, I'm not going to die on you too soon. I'm going to fight it."
Van der Westhuizen reportedly became the first South African to undergo the treatment, developed by United Kingdom neuroscientist Dr Steve Ray, two weeks ago.
Doctors injected some of his stem cells back into his body, with the hope that the cells would repair damaged muscle tissue.
Van der Westhuizen, who first realised there was something wrong with his right arm late last year, was diagnosed in July.
He played in South Africa's victorious 1995 Rugby World Cup team and at one stage held the record as the most capped Springbok player.
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