Sir Alex Ferguson does not believe referee Mark Clattenburg used "inappropriate language" towards Chelsea player John Mikel Obi.
The Blues during their at Stamford Bridge on Sunday.
"I don't believe he would make comments like that," said Ferguson. "I refuse to believe it. It's unthinkable."
Responding to Ferguson's remarks, Chelsea boss Roberto Di Matteo said: "He likes to talk about other clubs."
The former Italy international added: "We tend not to, so I'll leave it up to him.
"It doesn't really affect me too much to be honest.
"It's a free country where everybody has the freedom of speech.
"We take into consideration what other people say and use this for a motivational tool for ourselves."
Earlier this week, the Blues to the Football Association against 37-year-old Clattenburg.
The west London club said the complaint was made following a thorough investigation, which they say was led by outside legal counsel and used information from interviews with Blues players and staff.
Clattenburg maintains his innocence and neither of his assistants, nor the fourth official, support Chelsea's allegations.
United manager Ferguson, speaking ahead of his team's Premier League home game against Arsenal, added: "There is not a referee who would stoop to that. I'm convinced by that.
"I've never had a player come to me in the last 15 years and say a referee swore in a game - ever.
"The way we see the game today rather than how it was 25 years ago, it has completely changed. I played myself and I know that the banter which went on between referees and players 25 years ago is different to today."
Di Matteo does not expect the fallout of the last few days to hit performances and says he "still has faith" in referees despite this week's controversy.
"From what I can see and feel with my group and my players, once we get onto the training pitch, they are fully focused on training and getting ready for the games," he added.
"So, I really hope it's not going to affect us at all.
"I really hope referees won't treat Chelsea differently and I believe they won't. I have faith in them."
On Thursday, Arsenal manager Arsene Wenger voiced his concerns over Chelsea's decision to make the allegations public.
"My opinion is just, I prefer when I didn't behave well, that I have an explanation with the referee at the end of the game, or on another day, than going public with little proof," said the Frenchman, who stressed he was not fully aware of all the details surrounding the Clattenburg row.
"I'm not a great believer in making these stories public."
Fulham manager Martin Jol also echoed Ferguson's view about Chelsea's claims.
"If he said that, it would be stupid but I can't believe that he said it," said Jol.
Queens Park Rangers manager Mark Hughes called for the the matter to be resolved quickly.
"The situation with Mark Clattenburg, the authorities seem to have got involved as well and you don't want it to drag on," he said.
"You would like these things to be addressed very very quickly so people can be allowed to move on, if possible."
The Metropolitan Police also started an investigation into the alleged comments after receiving a complaint from a source outside the game.
Chelsea initially suggested Spanish midfielder Juan Mata had also been verbally abused by Clattenburg, before deciding there was insufficient evidence to support these claims.
The Newcastle-based official has been stood down for this weekend's round of matches.