The Spanish football federation (RFEF) said on Saturday that there would be no restrictions on players from outside the EU for the Super Cup, despite only three being allowed in squads for league matches.
Sevilla said they could withdraw from the game in Tangier, Morocco, if Barca name an "improper lineup".
"Sevilla FC is surprised by the RFEF's announcement 24 hours before the Super Cup," Sevilla said in a statement.
"It has said that as many non-EU players as desired can be registered. In their last statement for the 2018-2019 season, only three were due to be allowed, without exception.
"The club's legal department is studying the matter and should FC Barcelona line up with more than three non-EU players, it would present possible ground for withdrawal due to an improper line-up."
New signings Malcom, Arturo Vidal and Arthur will likely be Barca's three non-EU players on Sunday, although Brazilian centre-back Marlon has also travelled with the squad.
Sevilla qualified for the match as last season's Copa del Rey runners-up, after Barcelona won the league and cup double.
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