Arsenal midfielder Martin Odegaard admits David Luiz can be "ruthless" in training.
Odegaard has outlined the role his team-mate plays as a leader within the squad.
Asked to name Arsenal's best defender, the on-loan Real Madrid man replied: “I would say David Luiz.
"When you see him in training everyday, he's a great person, a great leader of the team and he's very important for us."
The attacking midfielder said Luiz is a pleasure to have around the squad - but insists he always means business when it's time to get on the pitch.
“He's a great guy, happy and smiling, making jokes. But when we're on the field then it's another face on," said the Norway international.
“That's what I admire most about him, when he goes onto the pitch, he changes his mentality to be completely focused and to be ruthless.
“He's not a nice guy any more!"
