A man has been racially abused and bashed unconscious by three men in what police have described as a "sickening" attack in Melbourne's inner south-east.

Police said the 33-year-old victim was racially abused by one of the group as he walked along Princess Street in Prahran just before 3:30am on Sunday.

The victim exchanged words with the men, before he was attacked in a nearby car park.

Police said they had CCTV footage of the attack showing the three men punching and kicking the victim in the head before he falls unconscious.

When he regained consciousness, his attackers knocked him out again.

Detective Senior Constable Katie Johnston said it was a brutal assault.

"I'm appalled at the viciousness of the assault. It's quite sickening to watch," she said.

"The victim is basically rendered unconscious on two occasions and the offenders continue to kick and punch him to the upper body and the head."

The victim is in hospital in a serious but stable condition.

Detective Johnston said the victim was able to give the information about the attack before he was taken away for treatment.

Police released images of three men they want to speak to about the incident.

They called on anyone with information to get in contact with them.