"I realise that I can compete with Messi and Ronaldo in the near future, if I put in some more effort," he told Het Laatste Nieuws.
"I don't know if I will ever reach their level. It'll be hard, they have incredible stats, but I accept the challenge.
"Of course I want to be the best in the world. Previously I was more worried about the game itself: football was just a game for me, I wanted to amuse myself and didn't bother what the people thought about me.
"Since I've been at Chelsea, I've become more aware of my qualities, I guess. Before I knew I was a good player, but not one of the better players in the world."
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