Arsène Wenger gave the 20-year-old his first-team debut in the League Cup last season and has since started him at Barcelona and Paris Saint-Germain.
“[I knew] when I took him in training a few times," said Wenger to arsenal.com.
“He is not the kind of player who impresses you at first. But when you look a bit deeper he is quick at connecting with other players. Quick analysis.
“Football is perception, decision-making and acting. The perception especially struck me. The perception he has of the game and the speed of his decision-making struck me.
“When you look at him at first there is nothing special there. But after when you look he is always connecting with others at a very high level and a very high pace. That's why I think he is improving.
“He has still a lot of work to do but he has something that is very important at the top level. Speed and an understanding of the game."