The Royal Spanish Football Federation (RFEF) announced ahead of the match that the two teams faced no nationality restrictions in compiling their squads, leaving Barca free to pick from their clutch of new South American recruits, Brazilian pair Arthur and Malcom and Chile's Arturo Vidal having arrived at Camp Nou in the off-season.
Sevilla had already been antagonised by the RFEF's decision to stage the Supercopa, traditionally a two-legged, home-and-away tie, as a one-off match in Tangier.
And the Andalusian club posted a message on Twitter on Saturday raising their concerns about Barca's potential line-up.
"Sevilla FC is surprised by the RFEF's statement 24 hours before the Super Cup," the tweet read.
"It has stated that as many non-EU players as desired can be registered, despite the fact that in their last notice for the 18/19 season, only three were due to be permitted, without exception.
"The club's legal department is studying the matter and should FC Barcelona submit a team with more than three non-EU players, it would present possible ground for the filing of a complaint on account of an improper line-up."
Sevilla's objections may prove unfounded, though. Widespread reports in the Spanish media claim Brazilian Philippe Coutinho has gained a Portuguese passport through his wife, easing Ernesto Valverde's selection constraints.
This will be the 32nd edition of the Supercopa, with the previous season's winners of La Liga facing off against the Copa del Rey champions.