The Basque side, trailing 3-0 from the first game in Bilbao last week, are set to be backed by almost 4,000 away fans in what promises to be a special occasion at Old Trafford on Thursday night, with the action kicking off at 20:00 BST.
Ernesto Valverde and his players are due to arrive in England on Wednesday afternoon, before the coach hosts a press conference in order to explain his selection.
There is big news as both of the Williams brothers are absent. The exciting forwards will be a big miss for Athletic Club, as Nico has failed to overcome groin issues that have dogged him recently, while Inaki has picked up a hamstring strain and failed to recover.