"I think the speed of his improvement has surprised a lot of people," he said. "He has developed enormously in the two seasons. I think he has surpassed expectations. He has far from reached his peak. If you look at other top quality players, players aged 22 to 23, who are absolutely brilliant - people like Messi and Ronaldo - you ask 'how can they improve?' They just do. They just get better. They see the game differently than they might have done three years earlier."