The 23-year-old has become a vital part of the Stamford Bridge squad since he joined from Lille in 2012 and although he has three years remaining on his original contract the club is keen to extend it.

Stories in the press on Tuesday morning suggested the Belgium international's deal could be worth as much as £50m, as the clubs looks to stave off reported interest from French side Paris Saint-Germain.

Speaking on the eve of the Champions League clash with Schalke, Mourinho said: "We have big hopes that he will go from a top player to reach higher levels.

"He's a kid that was always living on his natural talent. But from a certain moment he was starting to have some tactical education and mental education and it is big improvement he is having.

"Now his talent allows him to think about it and he can go from a top player to become one of the greats of his generation. We are proud he thinks Chelsea is the right environment for him.

"He's a player we want to keep. It's true Chelsea is trying to have an agreement for a new contract.

"It will be a question of time. It will end with a new contract.

"He wants to commit to us and we want to commit to him for the future."