A reveller claims he was punched outside Chicago Rock Café in Moulsham Street in an unprovoked assault.
The 24-year-old says he received bruising to the right side of his face as a result of the reported attack, which is said to have taken place at about 2.30am - close to closing time - on Sunday, April 20.
Police have found no evidence of the alleged attack on CCTV.
Anyone with information should call PC 3130 Simon Gray on 101 at Chelmsford police station.
