Chelsea boss Jose Mourinho believes new signing Jon Obi Mikel is among the best young players in the world.
Mikel previously signed a contract at Manchester United
Mikel signed in a £16m transfer on Saturday after a dispute with former club Lynn Oslo and Manchester United, who he had signed a contract for.
Mourinho said: "In Lassana Diarra, Jon Obi Mikel and Salomon Kalou we are speaking about the best young players in the world.
"We can teach him to be more complete, more intense and to defend better."
Mourinho added: "He's bright in the way he thinks about football, technically he's fantastic, and it's just a point to get the intensity of the English game.
"Everybody was in love when he started training, not just me but the players who were amazed at such a young boy coming from nowhere and training with us with such quality.
I like making the team play, get into the game, keep moving around
"You saw him in the African Cup playing like a giant in the middle of players like Jay-Jay Okocha, Joseph Yobo, Didier Drogba, Samuel Eto'o, at an absolutely unbelievable level. We know the level he can be.
Mikel will start training with Chelsea's other non-World Cup participants on July 17.
He told Chelsea TV: "Everybody's got his style of play. I'm a midfield player who just wants to go in there and do my stuff.
"I'm not a defensive player, I like making the team play, to get into the game, keep moving around, keep looking for the ball and make sure the team plays well.
"My next target is to start playing again. I've not been playing for a long time but I've been doing my thing to keep fit.
"I think I'm pretty fit but we will have to see in a match situation."