The stakes are so high going into the game at San Mames, as the Reds are targeting two trips to the Bilbao venue in May, with the ground also staging the final.
Athletic Club are currently fourth in La Liga and had no fixture this weekend, allowing them to fully prepare for what will be a tough test of Ruben Amorim's men.
Nonetheless, the incredible victory over Lyon in the previous round shows just how determined United are to win this trophy for a second time and earn a spot in next season's Champions League, despite the most challenging of campaigns.