Mancini was angered by the official not awarding a free-kick for a challenge on Pablo Zabaleta in the build-up to Adam Johnson's goal in the 1-0 defeat at Sunderland on Boxing Day.
The Italian said: "The referee ate too much for Christmas. He was not in good form. But that can happen after Christmas when they have a performance like that."
City are angry at the prospect of an FA charge, and Mancini's defence will be that, although he was bitterly disappointed about the manner of his side's defeat, he attempted to make light of his dissatisfaction at Friend's display.
Harry Redknapp is also facing action, with the FA contacting the Queens Park Rangers manager to ask him to explain his statements about referee Chris Foy following the 2-1 defeat to West Bromwich Albion on Boxing Day.
After the match, Redknapp said: "The linesman said it was murky down in that corner and he couldn't see [a potential Liam Ridgewell handball], so maybe he should go to an optician... it's just poor refereeing.
"I had him [Foy] at Stoke last year when I was Tottenham manager and he let three penalties go, so what's the point in talking to him?"
Redknapp said yesterday that Jose Bosingwa's future at QPR remains in doubt, despite the defender finally apologising to his team-mates for refusing to be a substitute against Fulham a fortnight ago.
The defender was fined two weeks' wages (pounds 130,000/ euros 159,000) over the incident and has not been in the squad since. Redknapp said: "We'll have to have a look and see how we go in January with it."
The manager was surprised at Bosingwa's reaction having invited his players to ask him the following Monday if they had queries about his team selection. "You don't expect someone to knock on your door a minute later and say: 'I'm not sitting on the bench.' I can't have it really."
Redknapp wants to bring in new signings as quickly as possible but admitted he has yet to tempt anyone to Loftus Road. "I wish I could say otherwise, I haven't got anything too much in the pipeline," he said.
Yet he believes that the opportunity to pull off what could be one of the Premier League's greatest escapes is the club's biggest draw. "You're looking for people who are willing to take on a challenge," Redknapp said.
"I say to the players come and have a go - if we get out of this, fantastic."