Chelsea have appealed for witnesses after fans prevented a black man from boarding a train in Paris on Tuesday, as well as for a separate incident outside the Parc des Princes which saw a number of Blues fans affected by tear gas.
Footage posted on the Guardian website, above, shows the man trying to board a Metro train at the Richelieu-Drouot station in the French capital, but he is blocked by what appears to be a group of Chelsea fans travelling to the Parc des Princes for the 1-1 Champions League draw with Paris Saint-Germain on Tuesday night.
The Paris prosecutor's office said it has opened an investigation, while Chelsea have warned that they are prepared to ban any fans involved in the incident.
The identities of the people in the video, including the victim, are not yet known, prosecutor's office spokeswoman Agnes Thibault-Lecuivre told The Associated Press.
It is also not confirmed whether the passengers were Chelsea supporters heading to the Champions League match, but both British and French police said on Wednesday they are trying to identify those involved in cooperation with the Metropolitan Police.
A statement on the club's official website on Wednesday read: "Chelsea Football Club is appealing for witnesses regarding the reported incident on public transport in Paris yesterday (Tuesday).
"To help us with our investigations and to identify those persons involved, we ask those who were present to forward their observations, in the strictest confidence, to customer.services@chelseafc.com."
In a video of the incident, the black man tries to board the train and is pushed away. He then pushes back and says in French "Can I get on or what?'' before again being shoved away.
The carriage, mixed with Parisian commuters and English football fans making their way to the game, is packed. But there is enough standing space for one more person, as is evident when the man steps inside before being pushed away the first time.
The group -- some of whom chanted "Chelsea, Chelsea, Chelsea'' -- then sing "we're racist, we're racist, and that's the way we like it.''
At about that time, several Paris transport officials walked past the group, but did not intervene, and the black woman left the adjacent carriage.
The club is also appealing for witnesses following a number of supporters being affected by tear gas outside the Parc des Princes before kickoff.
The club advised witnesses to email the same account, with an official statement reading: "We are emailing fans who purchased tickets directly from the club asking for witness accounts of the incident.
"The incident was brought to the attention of UEFA immediately and information we collect will form the basis of a report the club will send to UEFA."
Meanwhile, Diego Costa says it is vital for the club and the players to set an example in eradicating all forms of discrimination from football.
Ahead of Saturday's 'Game for Equality' match against Burnley, Costa told the club's official website: "It's very important, especially because of the magnitude of the club. Chelsea can set an example with regards to equality within the game.
"I know the club has been doing a lot of work in order to promote equality and take away discrimination. A lot of hard work has been done and it's hugely important.
"We work every day and we know we are a big example to children around the world.
"It's important to remember that we are all learning ourselves because we are not born with lots of knowledge. Children look up to us and that's where they learn their traits from, so we are very important in the process."
Information from Press Association and The Associated Press was used in this report.