Witnesses say two men were arguing in the car park at the Waltzing Matilda Hotel, in Heatherdale Road, Springvale South, when one was punched in the face just after 11pm.

The 24-year0old injured man fell to the ground and was unconscious when a passer-by raised the alarm.

The Springvale South man was conscious and sitting when Ambulance Victoria arrived to treat him but Ambulance Victoria spokesman John Mullen said the victim refused to be taken to hospital.

"We wanted to transport him but he decided he didn't want to go, we advised against it given his injuries," Mr Mullen said.

Friends of the man said they would take him to Monash Medical Centre, where police say he remains in a critical condition.

Police arrested a 20-year-old Endeavour Hills man at the scene and have interviewed him. He was released pending further inquiries.

Police believe the two men know each other.

Dandenong Crime Investigation Unit detectives are investigating and appealing for witnesses to come forward. They would like to speak to the driver of a dark-coloured vehicle that was in the area at the time of the incident.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or make a confidential report at www.crimestoppersvic.com.au