While Mancini believed the challenge to be worse than Vincent Kompany's on Nani over the weekend, Gerrard claimed that the Blues boss wanted Johnson to get sent off.
Kompany is currently serving a four-match ban after he was shown a red card during Sunday's FA Cup third-round tie against Manchester United.
"Steven Gerrard can say what he wants," said the Italian. "I said what I think. That is what I am used to doing. It is not important what Steven Gerrard or the other players have said."
The second leg takes place at Anfield on Wednesday, January 25.