A man has been left with serious injuries after he was reportedly assaulted by two security guards outside a licensed venue in Melbourne's CBD overnight.

It is believed the victim, a 23-year-old Yallambie man, may have been involved in a brawl with two security guards outside a venue on the corner of Downie Street and Flinders Lane, Melbourne, about 3am on Sunday.

Ambulance Victoria spokesman Ray Rowe said paramedics arrived at the scene about 3.20am, where they found the victim suffering from an upper-body injury. He was taken to the Royal Melbourne Hospital in a serious but stable condition.

Victoria Police spokeswoman Belinda Batty said officers arrested two men, a 23-year-old and a 35-year-old, at the scene. Police would not confirm if the two men were security guards. 

It is also believed the victim sought help from a man driving a green ute, possibly a Holden, on Flinders Lane at the time, Ms Batty said. 

Police ask that the driver of the ute, and anyone else with information about the attack, phone Crime Stoppers on 1800 333 000.