The man whose goal, in the closing stages of the game at Nottingham Forest in the previous round, took Erik ten Hag's team into the last eight, misses out on the opportunity to face our fiercest rivals.
Although he had been sidelined with an injury, the 32-year-old returned at the back end of January, and featured nine times since then.
Speaking before kick-off, the manager told ITV1: "It does [affect us] because Casemiro is very experienced and a very important player for us in organisation, also on the ball, he brings composure to the team and he can bring great passes to bring our frontline into great positions, especially with the three with their immense speed.