At 8.50pm on Monday 11 October, a man was trying to enter an occupied toilet on the train. He attempted to open it and was banging on the door.
A man came out of the toilet and the other man entered. A few seconds later the man opened the door of the toilet and an altercation broke out between them.
The man headbutted the victim, who then fell to the floor and he pressed his finger into his eyes. Other passengers intervened and separated them.
The victim attended the hospital for treatment to damage to his eyes.
Officers believe the man in the image may have information that could help their investigation.
If you recognise him or have any information, please contact BTP by texting 61016 or calling 0800 40 50 40 quoting reference 565 of 11/10/21.
Alternatively, you can call Crimestoppers anonymously on 0800 555 111.