"Prospect is committed to helping to eradicate racism in football and in society generally," the trade union, of which the referees' union is a member, said in a statement. "We will be making no further comment at this stage."
Clattenburg is waiting to hear whether the England Football Association will launch an investigation into allegations he made racist comments during Manchester United's 3-2 win.
Chelsea last night made a formal complaint to the match delegate, whose report was expected to arrive at FA headquarters Monday.
Mikel's agent and Chelsea did not comment Monday, but the club did confirm that it had decided against holding a press conference Tuesday to preview Wednesday night's Capital One Cup clash against United.
Chelsea's complaint against Clattenburg, 37, could hinge on the evidence of the assistant referees who would have heard every exchange, according to ex-referee Graham Poll.
"A referee's microphone is on open. Everything he says is heard by two assistants," Poll, who refereed 1,544 matches during his career and officiated at two World Cups, told BBC Radio 5 live. "So if Mark said something, the assistants would have heard it."
Former Premier League referee Jeff Winter said Clattenburg won't officiate a match again if the charges are proven true.
"I'm not saying referees should do it, but there seems to be one law for one set of people and one law for another, but this inference that racial language has been used is very, very serious," Winter said.
Information from Press Association was used in this report.