The Spain international, alongside Pau Victor, has been granted temporary registration by the Spanish national sports council, with the pair therefore able to take to the field until the CSD makes a ruling on the club's case against La Liga and RFEF.
Olmo is unlikely to start, but the attacker is set to be a huge option for the Catalan side off the bench in El Clasico.
Marc-Andre ter Stegen, Marc Bernal and Andreas Christensen will again miss out due to injury problems, but the latter is now close to being available for selection in what would be a huge fitness boost.
Wojciech Szczesny has now started successive matches for the Catalan giants and is again expected to feature between the sticks against Real Madrid, with the recent arrival seemingly the cup goalkeeper for Hansi Flick's side.
Ronald Araujo is currently with the squad in Saudi Arabia, but the Uruguay international is being heavily linked with a departure, with Juventus thought to be pushing to sign him, and a result, he may again not be involved in this fixture.
Lamine Yamal was on the scoresheet against Athletic Bilbao in Wednesday's semi-final, having recovered from an ankle problem, and the Spaniard is set for another start in the final third of the field.
Raphinha, Gavi and Robert Lewandowski are also set to be in the XI, but there will be no spot for Frenkie de Jong in midfield, with the Netherlands international currently out of favour under Flick.
Barcelona possible starting lineup: Szczesny; Kounde, Cubarsi, Martinez, Balde; Casado, Pedri; Yamal, Gavi, Raphinha; Lewandowski
Written by
Matt Law