The Belgium midfielder has scored 11 so far this season and the Portuguese has seen the 23-year-old move to another level during his second tenure with the Premier League high-fliers - scoring nine and assisting five goals.
"He trains much better, he concentrates much better. Tactically, he has had a big evolution. He understands how to put his qualities on the surface of the team. He understands the best way to hide his weaknesses."
All the more impressive is that he's doing all these things at such a young age, said the manager.
"He is 23 and now in his second season in England after an experience in France," he said. "He is playing in a Chelsea side trying to win the Premier League, also the Champions League, and is going to the World Cup with Belgium. He has in his hands all the tools to fill these gaps.
"Everyone knows he is a talented player, that he was that when he arrived here. But now he is trying to go to a different level, we are helping him and he is doing it step by step. Hopefully, the big talent can transform himself into the big player."