I think it is a confidence thing more than anything. He can still become a really good defender of course, and I do think he has the mentality for it, but I agree he does have it all to prove still.
@A-man Don't take offence of it or personal, he made a few mistakes but he'll be back on form soon. He will probably get opportunities in the team still with Ole and he has to prove to everyone he has what it takes. He still have to put in a performance against Messi in a few weeks, perfect opportunity to redeem himself.