The Borussia Dortmund midfielder impressed in their World Cup win against Iran.
Speaking to BBC TV about the 19-year-old midfielder, he said: "He is unbelievable. From when I first saw him to now, the footballing ability has always been there but he has gone from a boy to a man now, he is growing in himself.
"He has got everything a top quality midfielder needs and I have no doubt he is going to be a very, very important player for England in this tournament and for the future of English football.
"He is going to be a big part of it all.
"He has been involved in professional football from a very early age, you learn how to act and he is very mature, very confident.
"But he needs that confidence because he has all the ability in the world to be able to perform at a high level on the pitch. He needs that confidence."