Police are appealing for information after a report of a sexual assault at the Engine Shed night club at around 2.30am on May 19.
A man was reported to have kissed a 22-year-old woman and pulled up her skirt without her consent.
Lincolnshire Police arrested a 24-year-old man on suspicion of sexual assault and was later released on bail.
Any witnesses are urged to call the police to assist with their enquiry.
Information should be left for the attention of investigating Officer PC Graham Lawrence on 0300 111 0300.
Alternatively you can call Crimestoppers in confidence on 0800 555 111.