Barca landed their 30th crown last season and have lifted the trophy in each of the last four campaigns. What's more, they have been present in all but one of the last eight finals, which is a staggering record.
Ernesto Valverde's side will enter this match off the back of a 4-2 win over Sevilla at the weekend. The result has left them seven points clear of second-placed Atletico Madrid at the top of the table, with the treble very much on for the club this season.
Here, Sports Mole looks at how Barca could line up in El Clasico on Wednesday night.
Rafinha, Jasper Cillessen, Arthur and Thomas Vermaelen are still on the sidelines for Barca. Cillessen would have started between the sticks had he been fit, but the Dutchman's absence means that the club's number one goalkeeper Marc-Andre ter Stegen will feature.
Samuel Umtiti made his return from a knee injury against Sevilla, but it seems likely that Clement Lenglet will come back into the team for this match. Sergi Roberto, meanwhile, could replace Nelson Semedo at right-back with the latter struggling to perform at the weekend.