Police and the Football Association have launched formal investigations into the European champion's allegations Clattenburg used "inappropriate language" towards Mikel, something Press Association Sport understands the official strenuously denies.

Leading figures such as Manchester United manager Sir Alex Ferguson have had their say, backing 37-year-old Clattenburg.

And ex-Premier League referee Wilkes says the feelings of some of his former colleagues are so strong that they have started to discuss refusing to take charge of Chelsea`s games.

He told The Sun: "I keep in touch with a lot of the lads and there is such a strength of feeling about what is happening to Mark.

"I know a few referees who are even talking about boycotting Chelsea games because of all this.

"Remember, it's not the first time Chelsea have targeted a referee - there's been Anders Frisk and Graham Poll.

"And some refs are now saying enough is enough. It's no exaggeration to say the refs in this country have never felt lower.

"They are so disillusioned. They feel vulnerable, feel that they are being left isolated - that they are getting no backing, no support.

"They want to speak out themselves but are too frightened, they fear they will be sacked if they go public with their grievances.

"There have even been murmurings about strike action but that's very much the last resort.

"They'd much prefer to get around the table with the FA, PFA, the clubs and players to sort this out as quickly as possible."