The Metropolitan Police confirmed they had acted on what they described as a "complaint"
made by the Society of Black Lawyers after
It is understood the 37 year-old completely rejects the allegations against him - that he called Mikel a "monkey" and Mata a "Spanish t**t" - which are also the subject of a Football Association investigation.
A police statement read: "An investigation has been launched into alleged comments made during a football match between Chelsea FC and Manchester United FC at Stamford Bridge on 28 October 2012.
"This follows on from a complaint received by the Metropolitan Police Service on 29 October.
"Officers from Hammersmith & Fulham borough are in liaison with Chelsea Football Club and the Football Association.
"At this time, the MPS has not received any complaint from either Chelsea Football Club, or the Football Association.
"We continue to work in partnership with Chelsea Football Club and the Football Association in order to consider any allegation that is made in relation to the reported events."
The police probe came less than 24 hours after the FA launched its own investigation, which it must now decide whether to continue or postpone until after potential criminal proceedings are concluded.
The game's governing body came under fire for the way the John Terry case was allowed to drag out and will be desperate to avoid a similar saga with Clattenburg.
It is understood the referee had yet to be interviewed by the FA this morning but was ready to formally deny any wrongdoing having vowed to co-operate fully with any investigation.
He was said today to be shocked and angered at the allegations made against him and confident of clearing his name.
Should the FA continue with its probe, it is expected to interview Clattenburg, possibly after requesting a written account from him about what took place on Sunday.
Clattenburg has already filed what is known as an 'extraordinary incident report', which is understood mainly to deal with an alleged meeting that took place in the referees' room after full-time.
Sources claim that Chelsea manager Roberto Di Matteo, assistant manager Eddie Newton and chief executive Ron Gourlay were all present as Mikel angrily accused Clattenburg of abusing him.
The referee, his assistants and fourth official are understood to have been stunned by the claims, with Michael McDonough, Simon Long and Michael Jones denying hearing anything of that nature via the officials' microphone link-up.
Clattenburg's fellow professional referees were today thought to be as shocked and angered as their colleague over the allegations against him and were rallying around him.
It was unclear whether Clattenburg would elect to continue refereeing or take a break from the game while any investigation was pending but he accepted being stood down yesterday from officiating in the coming week.
Police became embroiled in a second high-profile football racism case last night after the man behind the mooted black players' breakaway union, Peter Herbert, sent a letter to the Metropolitan Police Service (MPS), which read: "The Society of Black Lawyers wishes to record the incident that took place at Chelsea FC.
"Our information is that racist remarks were directed at John Mikel Obi and at Juan Mata. If so, that is wholly unacceptable in any circumstances.
"Although this matter may be investigated by the FA, it is appropriate that the MPS independently see if a racially-aggravated offence has occurred."
It was unclear whether Mikel, Mata or Chelsea welcomed police involvement but they could be forgiven for being wary of it in the wake of the Terry case.
Clattenburg, who vowed on Sunday to co-operate fully with any investigation, was yesterday promised the "full support" of referees' union Prospect.