Bendito Mantato, who trained at Carrington with the senior group on Wednesday and was named in the travelling squad, has been added to the B list for the competition.
As he is a homegrown player, who has come through the ranks with the Reds, the 17-year-old is now eligible for the fixture at San Mames, which kicks off at 20:00 BST.
The versatile forward has impressed for the Under-18s and Under-21s this term and will be gaining valuable experience out in the Basque Country.
Mantato scored the extra-time winner in the dramatic FA Youth Cup quarter-final win at Arsenal's Emirates Stadium earlier in the season.