British Transport Police yesterday released a CCTV image of a man who they want to speak to about the incident.
They also urged any other station users with information or who saw the incident to come forward.
Investigating officer PC Fahd Khan said: “No-one should have to suffer such offensive abuse, particularly when they are just doing their job.”
The incident happened on Tuesday, August 16 just after 10.30pm when a man approached the barriers leading onto the station platforms.
He was trying to pass through without a ticket when the member of staff challenged him.
After being told he would need to buy a ticket, the man became racially abusive.
The man returned a short while later after buying a ticket and when he had passed through the barrier, he threw it at the victim.
PC Khan said: “After reviewing CCTV, we are today issuing an image of a man we want to speak to about the incident.
“The man in the images is someone who I believe has information about this incident. Who is he?”
Anyone with information is asked to contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference 149 of 31/8.
Information can also be passed anonymously to the independent charity Crimestoppers on 0800 555 111.