British Transport Police are seeking witnesses to the incident on the Piccadilly Line on Monday, the 31st of March, between 8.20am and 8.40am.
The victim asked a man to move bags and a buggy, prompting the suspect to punch him before leaving at Knightsbridge.
The man is described as black, with dreadlock hair, was wearing a grey tracksuit and was accompanied by a woman with a buggy and suitcase.
Anyone with information or who may have seen the incident is asked to contact BTP by texting 61016, or by calling 0800 40 50 40 quoting reference number 116 of 31 March.
Alternatively, call Crimestoppers anonymously on 0800 555 111.
