Barca have already been beaten at San Mames this season but face an Athletic side who aren’t in the greatest form and needed penalties to get past Tenerife and Elche in the last two rounds.
Here’s a look at how Barca might lineup tomorrow night:
Neto is still not back to full fitness after a sprained ankle which means Marc-Andre ter Stegen should continue between the sticks for Barca.
Gerard Pique is suspended for the weekend’s game against Real Betis which should mean he’ll start this one, except he trained away from the team in the gym on Wednesday which means he may have a problem.
Samuel Umtiti and Clement Lenglet are both fit and available, while Barca B’s Ronald Araujo could come into contention if Pique is ruled out.
Nelson Semedo was in fine form against Levante and may keep his place, with Jordi Alba or Junior Firpo featuring on the opposite flank.
Arturo Vidal is a slight doubt after missing out at the weekend with a bruised thigh, although he was back in training on Wednesday.
Sergio Busquets, Frenkie de Jong, Ivan Rakitic and Arthur are also fit and available, while B teamers Riqui Puig and Alex Collado may be hoping for some Copa minutes.
Injuries mean Barcelona really don’t have many options in attack other than Antoine Griezmann, Messi and Ansu Fati.
Griezmann has been enjoying the Copa del Rey this season for Barcelona, with three goals in his two games in the competition.
Quique Setien could turn to Barcelona B for attacking options if he does feel his forwards need a breather. Kike Saverio trained with the team on Wednesday and looks the most likely player to be called up.
Possible XI: Ter Stegen; Semedo, Pique, Umtiti, Alba; De Jong, Busquets, Arthur; Messi, Griezmann, Ansu.
How do you think Barcelona will line up against Athletic? Let us know your thoughts, predictions and teams in the comments below!