Manchester United striker Dimitar Berbatov cannot explain his cool persona.

He told manutd.com: "I don't know... this is just who I am. It's important to stay focused and cool and maybe don't show your emotion.

"You need to show that you are fully concentrated on the game. Inside I know what I am going through in moments during important games, but I don't like to show much emotion. I just stay focused on my game and I think it works."