He's just a babe. Plenty of time to come good.
Unfortunately I don’t think any player with such extreme physical problems is ever going to become a top player in the PL. He is made of glass and is never even available for selection. He might only be 21 still but the last 2 years have been a waste of time in developing him for the PL.
He was never fit during the first season here and last season he had a middling loan at a middling German team. As soon as he came back to English football and the demands of a PL training schedule he crocked himself again. Barring a miracle I think his career at this level is over already.