Recovery from brain injury is a marathon, not a sprint, says an expert from Brain Injury Australia as cricketer Phillip Hughes fights for his life.

Recovering from a brain injury is a marathon, says Brain Injury Australia spokesman Nick Rushworth, who has had his own a brush with death.

But that doesn't mean there is no hope for cricketer Phillip Hughes, he says.

"It could be that Phil is inside the bell curve and there could be some profound consequences," Mr Rushworth told AAP.

"Or he could be an outlier, he could be playing cricket at some time in the nearest future."

Hughes will undergo further scans on Wednesday as he fights for his life in an induced coma at Sydney's St Vincent's Hospital.

Hughes underwent surgery for a critical head injury sustained at the SCG on Tuesday afternoon.

A hard ball travelling at a high speed could injure the brain in a number of ways.

"The brain itself has the consistency of butter, it's encased in fluid and the skull has jagged edges and ridges on the inside and with that kind of force applied to the back of the head, there would have been some rupturing of blood vessels.

"Clearly what the brain surgery was trying to do was relive pressure on the brain from the collection of blood and fluid inside the brain as a result of a shearing and tearing of those kind of blood vessels."

Rushworth, who suffered a brain injury in a cycling accident in 1996, said no two brain injuries are the same.

"The only similarity is that I was also wearing a helmet and I took the full force of the impact just underneath the line of the helmet.

"I needed facial reconstruction surgery.

"Recovery from brain injury is a marathon, not a sprint."

AAP.