Chelsea manager, Frank Lampard has warned the club's supporters against singing offensive songs and chants against their city rivals.
Lampard gave the warning after the club's fans used derogatory chants against Tottenham and West Ham fans after their pre-season friendly with Reading.
Tottenham and West Ham fans were the targets of ugly chants from a section of Chelsea's travelling support at Reading on Sunday.
One song in particular, which celebrates Lampard's 200th goal for Chelsea against West Ham at Stamford Bridge back in 2013, describes the Hammers as 'pikeys' - a derogatory term used as a slur against English Gypsies and travellers of Irish heritage.
In a similar vein, songs referring to Tottenham's Jewish connections could also be heard in Berkshire.
Speaking after the game, which Chelsea won 4-3 thanks to goals from Ross Barkley, Kenedy and a double from Mason Mount, Lampard - himself a former West Ham player - said the club has worked hard over recent seasons to stamp out disparaging chants.
The 41-year-old former midfielder said he didn't want to hear such songs.
"The support for the fans was incredible," the ex-international told post match press conference.
"I didn't hear the song in question, and of course if there's a song in the modern day or any day that has offensive words I don't want to hear that.
"That's me saying that as a big Chelsea man who really appreciates the support and had it over the years.
"We don't want songs with offensive words. If the fans could sing other songs then I'll back that.
"We don't want to hear that. The club are very clear with the work we do off the pitch about anything that's offensive or prejudiced and we've made a big mark on that in modern years. We don't want that."