The incident occurred between 1am and 1.25am on Sunday, 4 August near Tesco Extra at Mall Avenue, Musselburgh.
During the altercation, a 22-year-old male was attacked by a group of men, all of whom were wearing formal attire.
The victim sustained a puncture wound to his left arm - understood to be a stab wound - and was taken to the Edinburgh Royal Infirmary by ambulance where he was treated and later released.
An eyewitness, who wishes to remain anonymous, told the Evening News that they had witnessed the aftermath of the altercation outside Eskmills bowling club.
They claimed that the attackers, who looked to be in their early 20s, were all smartly-dressed and could be heard bragging about the attack before fleeing the scene in a taxi.
Police say investigations are ongoing to establish whether a weapon, if any, was used in the attack.
Detective Constable Craig Dilworth from Dalkeith CID said, “We are investigating after a disturbance in the Musselburgh area left a man with a serious injury to his arm.
“We are continuing with our enquiries to establish the full circumstances of this assault and anyone who was in the area and witnessed what happened should contact police immediately.
“Likewise, anyone who can help us identify the suspects should also come forward.”
Anyone with information is requested to contact Dalkeith CID on ‘101’ quoting incident number 505 of the 4th of August. To report information anonymously, contact Crimestoppers on 0800 555 111.