A 58-year-old, from Beaconsfield, was arrested after launching an attack on a 45-year-old woman in a corridor at Bond Street station in the early hours of Saturday morning.
The suspect was seen to hit the woman and then the unknown man at around 2.20am as Night Tube services ran.
British Transport Police have launched an investigation into the attack and have urged the male victim to come forward.
A spokesman said: “An investigation has now been launched and police are keen to trace the man who was assaulted during this altercation. To date he has not made contact with police.
“Likewise, officers are keen to hear from anyone else who was at the station at the time or witnessed this assault. The victims injuries as a result of the assault were minor.”
The female victim suffered minor injuries in the attack.
The man has been released on bail until April 20.
Anyone with information is asked to send a text to 61016 or call 0800 40 50 40 quoting reference 49 of 25/03/2017.
Alternatively, contact Crimestoppers anonymously on 0800 555 111.