Chelsea ace Willian admits he's sorry that David Luiz left for Arsenal last month.
The midfielder is close to his fellow Brazilian.
He told Goal: "Regarding David Luiz, everyone knows he's a great friend of mine. One of the best I have in football.
"It's hard to see him wearing a red jersey, but we're still friends. From now on, we will have to face each other, I will have to do something against him.
"And if I score against Arsenal, of course I will celebrate the goal."
