Roberto Di Matteo who said the officials "ruined" the Premier League game on Sunday which saw the Blues slump to their first Premier League defeat of the season is only too aware that his side need to focus on the game not the row with Clattenburg
Branislav Ivanovic and Fernando Torres were both given red cards in the space of five minutes just after the hour in United's 3-2 win - with the Spaniard's dismissal for diving disputed by Chelsea. But the crux of the game came when, as alleged by Cheslea, the referee used an offensive racial term.
The club added there was insufficient evidence to suggest Juan Mata had also been verbally abused by the official.
Clattenburg maintains his innocence and neither of his assistants or the fourth official support Chelsea's allegations.
Chelsea's formal complaint is the latest stage in a process which began after Sunday's match.
"Following Sunday's Premier League game against Manchester United, club board members were quickly made aware, upon entering the home dressing room after the final whistle, that there were allegations of inappropriate language directed at Chelsea players by Mr Clattenburg during the game.
"Board members began establishing the details of the allegations, speaking to all relevant players and staff. After those initial interviews it was clear that the matter had to be reported.
"The correct protocol for doing so was to report the incidents to the match delegate, and the club took immediate steps to inform him as soon as he was available. It was not a decision the club took lightly."
Following the game the club complained to the match delegate, while on Tuesday the Metropolitan Police began an investigation after receiving a complaint from a source outside the game.
Newcastle-based Clattenburg, 37, took charge of his first Football League game aged only 25 in 2000.
He was promoted to the Premier League's Select Group four years later and the Fifa list in 2006.
Clattenburg, assistants Michael McDonough and Simon Long, and fourth official Mike Jones were reportedly stunned when they were confronted by an angry Mikel in the referees' room after the match at Stamford Bridge.
Clattenburg's colleagues, who were connected to him by microphones throughout the game, were all said to have denied hearing him abuse either player.
Meanwhile Mikel and Mata both featured in the starting eleven against United with Torres and Ivanovic suspened. John Terry also remains suspened. Sir Alex Ferguson made several changes with Ryan Giggs starting and Robin Van Persie, Wayne Rooney and Rio Ferdinand all rested. But that didn't stop the Reds taking a 2-1 half-time lead as we wrote.