He would play in the no.10 position or on the right in a 4-2-3-1. Why do you feel he wouldn't fit into a 4-2-3-1 and what position does he easily fit into in a 4-3-3 that he can't in a 4-2-3-1?
Playing just off of a centre forward (no.10, second striker, centre attacking midfielder - however you choose to describe it) is his best position and where he has established himself as a top class player. He has played from the right for France and used to get moved to that position at Atletico whenever they would switch to a three man midfield. Playing from there, he is less effective as it removes some of his freedom to roam around and find space but he is still a top player. He has played in these two positions consistently for years so I think it's quite clear where he would play for us in a 4-2-3-1 and 4-3-3.