David Luiz has been one of Chelsea's biggest positives since February after putting in impressive displays against Fulham and Manchester United. However, one aspect of his game that has caught the eye other than his attacking flair and defensive solidity has been his aggressive tackling which almost got him sent off in the 2-1 defeat of Manchester United.

It has led his manager Carlo Ancelotti to warn him to calm down.

Against United on Tuesday, Chelsea produced a battling second half performance to comeback from 1-0 down to win 2-1. Luiz was a key figure for the Blues, frequently venturing forward impressively before capping the performance with a deserved goal. However, he also administered clinical, deliberate fouls on Wayne Rooney and Javier Hernandez while already on a yellow card which, luckily for him, was not spotted by referee Martin Atkinson.

Ancelotti said, Luiz has to understand English football and be more calm on the pitch. With more experience of the game here, he can change his behavior. As an attacking force, he has been fantastic - as he proved when he scored on Tuesday - but, defensively, he needs to improve that side of his game.

A furious United manager, Sir Alex Ferguson, was charged with improper conduct after blasting the referee for missing the incident involving Luiz. However, Ancelotti was coy on his United counterpart's argument.

Ancelotti said, I know Sir Alex had an argument with the referee, but I don't want to comment. I have a fantastic relationship with Sir Alex and we spoke after the game. He was disappointed about the decisions of the referee but this is football - one coach will be happy after a game like this, the other one unhappy. We spoke briefly about this, but then about other things.

After a game you are not cold. You have all the emotions of the game. Sometimes you will speak about decisions. This is normal, I think.