A Sydney man is reportedly fighting for his life in hospital after being diagnosed with a strain of mad cow disease.

A Sydney man has reportedly become the "one in one million" to be diagnosed with a variant of mad cow disease.

A friend of Frank Burton told the Ten Network the 63-year-old is in isolation at the Royal Prince Alfred Hospital and fighting for his life.

Mr Burton has reportedly been diagnosed with Creutzfeldt-Jakob disease, which belongs to a group of diseases that also includes mad cow's disease.

However, unlike mad cow's disease, Creutzfeldt-Jakob does not come from contaminated meat.

"It's just bizarre ... it's just terrifying," Mr Burton's friend Peter Kogoy told the network.

"He can't dress himself, he can't feed himself and is in need of 24/7 care."

Doctors have no idea how Mr Burton, a former Sydney Swans chief financial officer, contracted the disease, Mr Kogoy said.

According to the National Institute of Neurological Disorders and Stroke, the disease is a rare fatal brain disorder that affects one person in every one million a year.

Symptoms include failing memory, lack of co-ordination and 90 per cent of patients die within one year.

Creutzfeldt-Jakob disease cannot be transmitted through the air or by touching people but can be spread through "exposure to brain tissue and spinal cord fluid", the institute states.

RPA hospital has been contacted for comment.