The Londoners have lodged a formal complaint with the FA after alleging Clattenburg spoke out of turn to John Obi Mikel during Sunday's stormy Barclays Premier League clash against Manchester United at Stamford Bridge.
Chelsea have submitted a dossier which contains accounts given by players, who claim the 37-year-old whistler used a "racist" term.
Police are also investigating the matter.
Clattenburg denies the allegation and it is understood that assistant referees Michael McDonough and Simon Long, and fourth official Michael Jones, also believe he is innocent.
It is understood the trio did not hear anything untoward from the referee during the match on their linked headsets and are expected to say as much in any testimony.
Other well-respected current and former referees will offer positive character references for Clattenburg's defence if it is decided the County Durham official has a case to answer to the FA or police.
Meanwhile, West Ham manager Sam Allardyce expressed his dismay that police have become involved in another high-profile footballing matter.
Allardyce said: "I think if every incident is going to end up in the police's hands then it is going to be sad for the game of football in general.
"Over the last however many years as a manager I've never heard one referee give a bad comment to a player.
"So I found it a very strange thing that has been reported but only the authorities can decide if it has or hasn't happened."
