The Belgian is suspended for four matches after second red of the season, and his manager is upset his appeal failed following dismissal against Manchester United in the FA Cup
"I watched three or four players in the Premier League last week do tackles worse than Vinnie, and with the same referee," Mancini told reporters. "He did nothing, no yellow card, nothing."
"In 30 years I have never seen a sending off for a tackle like this. I can't understand it. Vinnie took the ball, he did nothing [wrong].
The Manchester City captain received his marching orders for a challenge on Nani in his side’s 3-2 defeat at the Etihad Stadium, resulting in a four-match ban as it was his second red card of the season.
He will now be unavailable for both legs of City’s League Cup semifinal against Liverpool as the Citizens look to book another trip to Wembley after its triumph in the FA Cup last season.
His suspension will be a blow for Mancini with Kolo Toure going off to the Africn Cup of Nations and the Italian is frustrated unsure as to why the club’s appeal over Kompany’s red card was not successful.
"If there was danger then Nani, who was the player nearest the ball, probably would have said something about this, especially to the referee. But he didn't say anything," he said.
"It's strange because in England the referee makes incredible decisions. Sometimes, they send off for nothing."
"This is strange, I don't understand."
Mancini has been mired in controversy in the past few weeks, firstly by appearing to try and get Martin Skrtel sent off for fouling Yaya Toure and then criticizing Wayne Rooney for appealing to referee Chris Foy before Kompany’s red card.
But the City boss has defended his actions, claiming it was natural to want retribution after seeing Gareth Barry sent off against Liverpool.
Mancini said: "Yeah, I did it. All the people were saying, 'Apologize, apologize, because in England we don't do this', so I apologized.
"But this is normal because, five minutes before, there was a red card for Gareth Barry for nothing.
"In Italy, it's normal [to do this]. We're different."