It happened at around 3.10pm on Monday, June 30, as a man in his 50s was walking towards the Central Line escalators.
Another man walked past him and began shouting and swearing, leading to a verbal altercation that quickly turned physical at the bottom of the escalators.
The victim was placed in a headlock and lost consciousness. The other man then fled the scene and boarded a Central Line train.
British Transport Police have released an image of a man they want to speak to, saying he may have information that could help with their investigation.
Anyone who recognises him, or who witnessed the incident, is asked to text 61016 quoting reference 391 of 30 June.
You can also contact Crimestoppers anonymously on 0800 555 111.
