It is a pity for the lad but the question is will it seriously weaken England? I suspect like many on here, we would have loved the All Blacks to have taken on England. England would probably win the battle up front but would spill a pass thus handing possession to NZ who can strike from just about anywhere on the pitch and score in one phase such is the speed they move the ball.
Will losing Itoje seriously weaken England? You are kidding, right? That's the equivalent of saying "would losing Virgil seriously weaken Saints".