Kompany, who will now serve a four-game ban if City fail in their intended appeal, won the ball but was shown a straight red card by referee Chris Foy for lunging in two-footed at Nani.
Ferguson said: "It was a sending-off.
"It was a two-footed tackle. I have seen him do it before.
"He has got off with it in the past. But if Nani gets caught, he has a problem. It was a real bad one."