The future of Olmo and young forward Pau Victor at the Catalan giants has been on hold over a financial and administrative limbo that prevented their registration beyond 2024.
Debt-laden Barcelona registered their star signing Olmo last summer without breaching La Liga's budget rules after defender Andreas Christensen was injured in August.
The Blaugrana lost two court cases seeking an extension of the registrations to the end of the season and La Liga struck Olmo and Victor off the official squad list on January 1.
Barcelona applied for new licences to the Spanish football federation (RFEF) and Spanish media said they had sold VIP seats at the future Camp Nou to generate 100 million euros ($103 million) that would increase their budget and facilitate the registrations.
La Liga has raised Barcelona's squad budget cap after the club met the financial rules on Friday and sent the relevant paperwork, the league and RFEF said in a statement on Saturday.
But the joint commission handling Olmo and Victor's applications agreed not to grant the licences due to RFEF rules which "prevent a player whose licence is cancelled from obtaining a licence in the same team" during the same season.
Barcelona said in a statement that they would appeal the decision at the High Council for Sports.
Club president Joan Laporta, who has faced heavy criticism for his handling of the affair, has spoken with Olmo and Victor "to calm them", the statement added.
Olmo's contract, initially set to run until 2030, includes a clause that would release him if he cannot be registered, according to Spanish media.
Olmo and Victor were absent from Barcelona coach Hansi Flick's squad list for the Copa del Rey tie at fourth-tier Barbastro on Saturday.
