- Video report by ITV News Reporter Richard Pallot
Chelsea have promised to take the strongest possible action against any supporters found to have sung an anti-Semitic chant on Thursday night in Budapest
The incident comes just days after four fans were suspended for abusing Manchester City's Raheem Sterling.
Minutes into Thursday Europa League clash with Vidi, which was drawn 2-2, a vocal minority of Chelsea supporters were heard singing a derogatory chant about Tottenham supporters, featuring anti-Semitic language.
Chelsea and the Metropolitan Police opened investigations after alleged racist abuse was directed at Manchester City's Sterling by a section of home supporters during last Saturday's match at Stamford Bridge.
In January Chelsea launched a campaign to raise awareness and educate about anti-Semitism in football and the club, including owner Roman Abramovich, who is Jewish, is disgusted at the latest incident.
A Chelsea spokesman said: "Anti-Semitism and any other kind of race-related or religious hatred is abhorrent to this club and the overwhelming majority of our fans. It has no place at Chelsea or in any of our communities.
"We have stated this loud and clear on many occasions from the owner, the board, coaches and players.
"Any individuals that can't summon the brainpower to comprehend this simple message and are found to have shamed the club by used using anti-Semitic or racist words or actions will face the strongest possible action from the club."
The Sterling incident overshadowed Chelsea's 2-0 Premier League win over last season's champions City and the latest incident is sure to be investigated by UEFA, who said it is awaiting the referee's report.