Melbourne Crime Investigation Unit detectives are investigating an assault in the CBD last night, Victoria Police say.
It is believed a man was walking back to his accommodation about 9.30pm when he was followed by an unknown male.
The man followed the victim into the foyer area of the Spencer Street building and punched him to the back of the head.
The victim lost consciousness and fell to the ground while the offender continued to yell at him before leaving the building.
The 50-year-old Ballarat man was treated for lacerations, possible broken jaw and bruising and has been released from hospital.
The offender is perceived to be Caucasian with a medium build, beard, aged in his 30s and had shaved brown hair.
Investigators have released CCTV and images of a man they believe may be able to assist with their enquiries.
Anyone with information is urged to contact Crime Stoppers.