The 27-year-old had been out with friends earlier in the evening but is believed to have been walking alone on West High Street when he got into a fight with an unidentified person.

The altercation happened at the corner of Lyster and West High streets at about 10.15pm, according to NSW police media.

"It appears to be a one punch-style attack and unfortunately he's then hit his head and that's where the injuries have been sustained," said Grafton local area command Inspector Joanne Reid.

She said police were appealing for information from any witnesses that may have been in the area.

"At this stage we're tracing his movements after leaving the licensed premises and trying to get a clearer picture of what happened," she said.

"We're canvassing local businesses, but most of them are closed for the long weekend."

The assailant was last seen running south down Lyster Street, according to police. They have not been able to obtain a description of the person, although he is believed to be a man, according to Inspector Reid.

Anyone with information should contact Crime Stoppers on 1800 333 000.

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