I think the guy will be great but he does need to improve on them mistakes.
Its not the fact hat he gives the ball away, everybody gives the ball away sometimes even Xavi. Its how and where he gives it away. Two examples to illustrate my point of the top of my head, one in the first game against England he had the ball in the centre and played a pass first time without looking to Montoya and he hit either Welbeck or Sturridge right in the chest and then that forward launched an attack (nothing came of it but thats not the point) and then tonight in the first half he got closed down by one of the midfielders and tried to roll the ball backwards to turn the defender and lost the ball and then Ukraine were able to launch an attack.
Now IMO there is nothing wrong with losing the ball in the attacking third when trying a through ball or something, it happens all the time in football but there are certain situations where keeping possession and doing something simple like playing a 5 yard pass to a teammate is better, the second example up there is one of those. Dudyk or whatever the left backs name is had moved past thiago (out of postion for himself defensively but in good position for an attack) and when something like that happens it is paramount that possession is kept,
if the opposition wins the ball there defenders will find themselves in a position where they are outnumbered on the counter attack.
Now nothing came of either of those mistakes but in the CL and against Real the margin for error is very small and mistakes like those end in goals. But of course these are mistakes that young guys make and mistakes that as they get more experienced they stop making so I'm not hating on him it's just what I think is stopping him from moving from the good young player that he is to a great first team player (or world class player) that I think he will be.
Sorry for the long post