Chelsea have assured they will take "the strongest possible action" against any supporters guilty of racist abuse after a video appeared to show fans targeting Mohamed Salah.
Social media footage before Thursday's Europa League game at Slavia Prague suggested a small number of travelling fans were aiming racist chants at former player Salah, now at Liverpool.
Chelsea are set to face Liverpool on Sunday and the Stamford Bridge outfit promised to investigate an incident described as an "embarrassment".
"Chelsea FC finds all forms of discriminatory behaviour abhorrent and where there is clear evidence of Chelsea season ticket holders or members involved in such behaviour, we will take the strongest possible action against them," a statement read.
"Such individuals are an embarrassment to the vast majority of Chelsea supporters who won't tolerate them in their club."
A statement from Liverpool read: "The video circulating online, showing vile discriminatory chants being aimed at one of our players, is dangerous and disturbing.
"Already this season, we have seen repulsive discriminatory abuse inside stadiums in England, Europe and across the world; abuse that was captured on devices and put into the public domain. We have also witnessed numerous hateful attacks on social media.
"This behaviour needs to be called out for what it is - unadulterated bigotry.
"Liverpool Football Club believes it is the responsibility of those in positions of authority, following proper process, to act urgently to identify and then punish anyone committing a hate crime.
"There is no place for this behaviour in football, there is no place for it in society. A crime of this nature has more victims than any individual it is aimed at and, as such, collective and decisive action is needed to address it.
"As pertains to this latest incident, the club is working with Merseyside Police to ascertain the facts around this footage with the aim of identifying individuals featuring in it.
"In addition, we are working directly with Chelsea Football Club on the matter. We thank them for their condemnation and a commitment to act urgently to identify any individuals responsible."
Anti-racism organisation Kick It Out posted the footage on Twitter alongside a short message: "It's not on the terraces, but it's still a disgrace.
"We don't want fans like that anywhere near our game. We will be liaising with Chelsea to ensure those involved are identified and punished swiftly and effectively."
Chelsea complained after alleged racist abuse was directed at teenager Callum Hudson-Odoi in their previous European tie against Dynamo Kiev.