Officers want to speak to anyone who witnessed, or has information about, an assault that took place in Chesterfield town centre.
The victim, a 19-year-old from Chesterfield, was left with injuries to his face after being punched by an unknown man.
The incident took place close to the Portland Hotel in West Bars at around 12.30am on Saturday, January 26.
If you have any information that could help the investigation, police would like you to contact them using a non-emergency method.
Quote the reference number 19*43477 and name of the officer in the case, PC Gill, in any correspondence.
You can also call Crimestoppers anonymously on 0800 555 111.
In the event of an emergency you should always call 999.