A medical expert is casting doubt on plans to conduct the world's first head transplant.

Italian surgeon Sergio Canavero wants to do the ground-breaking surgery in two years.

Now a 30-year-old Russian man has announced he will have the transplant done, after suffering from a terminal muscle wasting disorder.

Graeme Hammond-Tooke from Otago University's School of Medicine, says it's likely to be many decades away.

"The real problem is connecting the spinal cord up. In reality we can't do that yet. A lot of research is going into this because of spinal cord injuries but at the moment it's just science fiction."