The only thing that worries me about him is constant injury problems that he has. Wouldn't like to see another Diaby or Wilshere at Arsenal
More likely to be caused by growth. He hasn't suffered a fracture. His injuries are muscle related and he has spent a good while over the summer rehabbing and rebalancing. The groin strain was probably just a niggle while returning to first team intensity. Something we should expect Ballerina, Holding and Tierney to suffer.
Honestly though, ESR is something else. Ceballos is keeping it warm for him because when ESR explodes this team will receive a different dimension. His shooting technique is incredible.