I can only speak from experience but he was one of the most dangerous players I have ever played against. Barcelona players are not scared easily but I can tell you that when we played Arsenal last season he truly worried us. When we were playing Arsenal at the Emirates we were so in control of the game at 2-0, with all respect Arsenal were not even in the game. Then Theo came on and changed the game. He pretty much single-handedly salvaged a draw that night.