Rumor seems to be that Nastasic is on his way out of MCFC with them buying Mangala. He wouldn't be a bad option for us, still only 21 as well.
Great player, and also very athletic to make him compatible with Poch's high line. His wages probably aren't as high as a typical City player's either. Would be an excellent acquisition if we could get him at a decent price.
Hell, for his age, experience, and talent, I think he'd be worth the 15-20 mil if City ask for it.