We have Rojo, so center back is less of a priority now. Far from ideal still, but definitely less of an issue than midfield.
Still, I think the midfield can still get by this season, sounds ridiculous, but it's possible, and for me, signing Di Maria would solve far more issues than people seem to think it would. He's creative, extremely fast, works hard and can play in a three man midfield or on the right wing, two areas we're desperately lacking in. He's also probably one of the ten best players in the world. He's too good not to buy, imo.