"He's obviously a good young player and an exciting talent to have at the club. He's a different sort of player maybe to what we already have," he told the club's website.
"He played really well against us two seasons ago, scoring two goals at the Madejski Stadium. He didn't really have that many games for Chelsea last year but he's a great player and I'm really looking forward to playing alongside him.
"He has got a good engine, he can tackle, he can pass. He is just a typical box to box midfielder, a top class player."