The Italy international was dismissed 18 minutes after coming on as a second-half substitute for two bookable offences.
"It is not correct, the [second] yellow card. I do not agree with this yellow card," said the City boss.
"The referee didn't want to get a yellow card out, he did nothing for the yellow card.
"I think every time Mario does something many players provoke him.
"I think the referee gave a free-kick but didn't want to give a yellow card until all the Liverpool players complained.
"I watched the replay and for me it is nothing.
"This situation in the Premier League - there are a lot in every game; I don't think all are yellow cards.
"He moved his arm and Skrtel was like a young player and I don't think that was good.
"Mario should pay attention because he knows many players provoke him and this is not correct.
"Because of his red card we conceded a few chances from Liverpool."