Police and the Football Association are investigating an allegation that Clattenburg used "inappropriate language" towards John Obi Mikel in last weekend's stormy clash against United at Stamford Bridge. It is understood that the official strenuously denies any wrongdoing.
Chelsea have submitted a dossier of evidence to the FA containing accounts from players, who allege Clattenburg used a term which has been interpreted as racist, but Ferguson has defended the official.
Ferguson said: "I don't believe Mark Clattenburg would make any comments like that. I refuse to believe it.
"I think it is unthinkable in the modern climate. I just don't believe it - simple as that.
"There is no way a referee would stoop to that, I am convinced of that."
Ferguson has infamously had many run-ins with referees during his near 26-year reign at Old Trafford but he believes in the integrity of the officials.
He said: "I think in the modern game, the way we see the game today [Friday] rather than how it was 25 years ago, it has completely changed.
"I played myself and I know the banter that went on between referees and players 25 years ago is different from today [Friday].
"I have never heard a player come to me in the last 15 years and say a referee has sworn at them during a game, ever.
"So, that is where I stand. I don't believe it."
Press Association Sport understands Clattenburg will receive the full backing of his fellow officials during any investigations.
Assistant referees Michael McDonough and Simon Long, and fourth official Michael Jones did not hear anything untoward said on their linked headsets and are expected to say as much in any testimony.
Reacting to Ferguson's intervention, Di Matteo said this afternoon [Friday]: "It's a free country and everybody can say what they want.
"He likes to talk about other clubs. We tend not to."
"Nothing new to us," Di Matteo said of the attacks.
"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."
Di Matteo insisted Chelsea had done everything by the book during the Clattenburg affair but was prevented going into more detail by the club's refusal to discuss ongoing investigations.
A club spokesman said: "Around the whole evening and the incidents that have now gone on to FA and police investigation, we just need to not comment on that and let the investigation take its course."
The Blues are past masters at thriving in adversity but perhaps nothing as serious as this.
Di Matteo said: "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.
"So, I really hope it's not going to affect us at all."
Terry appeared to cope well with his own year-long racism scandal and Di Matteo was confident Mikel also would not buckle under the pressure of the formal allegation that has been made on his behalf by the club.
The Italian said: "I've spoken with the player and he's fine.
"He's a very strong character and has a very strong personality. I think he's shown that as well in his performances.
"He's been able to play and play well as well under this kind of pressure.
"So, from what I can see, he's dealing with all these issues in a good manner."