A man believed to be a Chelsea fan has been arrested on suspicion of racially abusing a woman, police said.
The man, 48, was taken into custody on Saturday evening, hours after the club's Premier League match.
The arrest came shortly after a group of Chelsea supporters were allegedly embroiled in racist chanting on a train back from the 0-0 draw against Norwich City.
A British Transport Police spokesman said: "Around 8.20pm on Saturday 21 January, a 48-year-old man, believed to be a Chelsea supporter, was arrested at Liverpool Street on suspicion of racially abusing a woman and was taken into custody.
"Separately, just before 6pm, police were made aware of another incident involving Chelsea fans on board the 1600 Norwich to London Liverpool Street service. At this stage, no arrests have been made in connection with the incident."
Officers are still looking for other people involved in the alleged incident.
Chelsea has vowed to take action against any fans proved to be involved in racist chanting.
A statement on the club's website said: "Chelsea Football Club is concerned to hear that a small number of fans travelling back by train from Norwich were alleged to be involved in racist chants and comment.
"We are working to help the relevant authorities identify those responsible and will take the strongest possible action should these allegations prove to be true.
"The club, like the overwhelming majority of our fans, strongly believe that all forms of discrimination are abhorrent and have absolutely no place in society."