A 19-year-old man who was about to start his dream job as an apprentice tradesman has been left blind in one eye after what police describe as cowardly, unprovoked assault.

The victim, who does not want to be named, was out with friends at the Royal Melbourne Hotel on February 17 when he struck up a conversation with a man in his 20s.

He was having what he called "a pleasant conversation" with the man when he left to go to the toilet.

He was followed inside where the man allegedly confronted him with a metal spike, described as a meat thermometer, and demanded his wallet and phone.

"He eventually snatched my sunnies and then I realised yeah this is for real," he said.

"I said, Just go your own way'. I walked off and he's come past and hit me."

The force of the blow severed his optic nerve and it is unlikely his vision in that eye will ever improve.

'It's ruined a lot of things for me'

Detective Senior Constable Jodie Hill from the Victoria Police robbery taskforce said it was an unprovoked attack.

"This unknown male has then followed … [him] and he's come up beside him and punched [him] in the face with a backward-motion fist up to his right eye," she said.

"[He] has suffered complete [vision] loss out of his right eye instantly and he hasn't been able to see out of his right eye since.

"He had bilateral fractures down each side of his nose."

The suspect fled out a back door and walked into nearby Southern Cross railway station.

He is described as being about 20 years old, with a medium to solid build, with long, dark, curly hair

He was wearing a black baseball cap, a muscle top, jeans and maroon runners.

Police released CCTV images of the man and want anyone who knows him to contact Crime Stoppers.

"It's just a coward punch and it's serious. It's one punch to the face and he's lost sight in his eye," Detective Senior Constable Hill said.

The victim said he was just about to start his dream job but he might now not be able to go ahead with it.

"I'm really upset — it's ruined a lot of things for me," he said.

"I used to race go-carts and I can't do that now. He's changed my life."

He believed the suspect was drug-affected.