A 23-year-old Perth man says he remembers nothing of an alleged one-punch attack which left him with brain and head injuries, until he woke up with pieces of his teeth in his mouth.

Tristan Ceccato was drinking with friends at Perth's Amplifier Bar early this morning when he was allegedly attacked.

The assault caused him to hit his head on a table and then the brick pavement, knocking him unconscious.

"The last thing I remember was walking out from a toilet with a friend and apparently that is when the incident happened, which I remember nothing of," he said.

"The next thing I remember was waking up with ambulance paramedics around me and friends and getting teeth out of my mouth."

The attack has left Mr Ceccato with bleeding on his brain, three broken teeth, facial stitches and a swollen jaw.

"The scan on my brain said there was a bit of bleeding at the front of my brain, nothing too severe but they are definitely going to be monitoring," he said.

Mr Ceccato, a health economist, said he was preparing to leave the bar when he was hit.

He was celebrating his last weekend in Perth before travelling to Canberra to start a new job.

He said he felt incredibly lucky that his injuries were not more severe.

"After hearing a lot about these one punch things, never really thinking it was something that would happen to me or one of my friends," he said.

"[You] sort of realise how vulnerable you are ... it's just disgusting."

Nollamara man Brent Robert Johnston, 21, appeared in court this morning, charged with causing grievous bodily harm over the attack.

He did not apply for bail, and his family wept at the back of the court as he was remanded in custody.

He will face the Perth Magistrates Court on January 29.