Ian Marshall, 67, was working at an out-paddock on the Cobden-Scotts Creek Road shortly after 6pm when the accident occurred.

Ambulances attended the scene and were quickly followed by the south-west emergency helicopter, which flew Mr Marshall to the Royal Melbourne Hospital.

Intensive care flight paramedic Shaun Whitmore said Mr Marshall suffered extensive fractures.

"Despite the injuries, the man was quite calm but in a bit of pain," he said.

"We put a drip in his arm and gave him some morphine to make him more comfortable for the flight to Melbourne.

"He was also given some fluid through the drip which helped stabilise his blood pressure."

It is understood the cow rolled on Mr Marshall's upper body and head as he tried to free it from a piece of wire connected to a fence.

Ambulance Victoria spokesman John Mullen said the man had possible fractures to his cheekbone, eye socket, jaw and ribs.

"Because of the nature of the accident he was also fitted with a neck brace as a precaution," Mr Mullen said.

"Five hundred kilos of cow rolling on you can do some decent damage.

Melbourne media initially reported the cow had kicked Mr Marshall in the face.

It is believed Mr Marshall's son was with him at the time and raised the alarm.

The emergency helicopter, which neighbours praised for its prompt arrival, landed in a nearby paddock and Mr Marshall was transported to it by ambulance.