Chelsea chairman Bruce Buck has accused some of the clubs fans of sending abuse bordering on racism after Avram Grant replaced Jose Mourinho at Stamford Bridge.
Chelsea's decision to replace the Portuguese coach with the 52-year-old Israeli has spawned a number of anti-Semitic comments which Buck says are unacceptable.
Buck's latest revelations arrived on the same day that Chelsea's season showed no signs of improving.
Their goalless draw against Fulham, Grant's first league game in charge of the Blues, was their fourth consecutive match without scoring.
But although they stretched their unbeaten home league record to 67 matches, Grant's problems were compounded with a serious injury to captain John Terry and a red card in the second half for returning striker Didier Drogba.
Terry saw a specialist last night and is to undergo an operation on a depressed fracture of the cheekbone after he was elbowed by Fulham's Clint Dempsey in the third minute.
Terry continued until half-time but was then substituted by Grant and the player's injury looks certain to keep him out for some considerable time.
He is unlikely to be fit in time for England's Euro 2008 qualifiers against Estonia and Russia despite suggestions from Chelsea staff that he will be able to return to training almost immediately.
Drogba will be suspended for one game following his dismissal for a second bookable offence but Buck is equally concerned with the reaction to Grant's arrival.
The fans chanted Jose Mourinho's name during the second half and even the club's billionaire owner Roman Abramovich, who sat with the fans in the upper tier of the Shed stand instead of his private box, was forced to endure their taunts.
But the sinister element of the near racist backlash following Grant's arrival is something Buck is determined to end.
Buck declared: 'We welcome all constructive points of view. But there have been a few which could be viewed as racist and anti-Semitic and that must stop immediately.
'This is one thing we will not tolerate, whether in written correspondence, on the chat pages, on posters or banners, or through singing and chanting.
'It unfairly smears the reputation of the vast majority of the Chelsea fans who rightly do not want to be associated with such activity.'
The anti-Semitic comments were aimed at upsetting Grant whose Polish father Meir, 80, is a holocaust survivor.
On the football front, Grant had promised the Chelsea fans a new attacking style but even with the fit again Drogba, they failed to find the net.
But the injury to Terry and Drogba's sending off did not help although Fulham's dogged determination almost brought them all three points when Petr Cech made a fine save to deny Paul Konchesky a winner five minutes from time.
Chelsea were guilty of squandering numerous chances with Salomon Kalou and Andriy Shevchenko the biggest culprits but Grant faces more injury problems ahead of their trip to Valencia in the Champions League this week.
Terry is almost certain to be missing following his cheekbone surgery while midfielder Michael Essien and England winger Shaun Wright-Phillips remain doubtful.