A man was only able to report being seriously assaulted to police after leaving hospital following reconstructive surgery on his face.
Officers are investigating the offence which occurred in Knaresborough on Saturday, March 31.
It is believed to have occurred in the ginnel leading to Park Place, between the High Street and Park Row, at about 11.45pm.
A North Yorkshire Police spokesperson said: "A man in his mid-thirties was seriously assaulted, and was only able to report the assault yesterday due to being in hospital since the night of the assault having facial reconstructive surgery."
"Three men were believed to be in the area at the time of the assault, and it may be that they – or somebody else – may have information that could assist the police investigation.
"To jog people’s memory, the assault took place after the Anthony Joshua boxing match."
If anyone has any information they are asked to call the Serious Crime Team at Harrogate Police Station via 101, quoting incident number 12180060707.