It remains to be seen what's their final squad for the game.
On Saturday, the Spanish football federation clarified that, unlike in La Liga, there were no restrictions on non-EU players for the Spanish Super Cup because the game was considered "not professional".
Releasing a statement, Sevilla said, "Sevilla FC is surprised by the RFEF's announcement 24 hours before the Super Cup".
Messi, who will don the captain's armband for the first time after the departure of Andrés Iniesta to Vissel Kobe during the summer, will also overtake the midfield maestro as the player with the most titles for Barcelona.
With former captains Xavi and Iniesta, the architects of Barça's tiki-taka years of domestic and European hegemony, now departed Messi will be the undisputed leader of the side in 2018-19 as Valverde seeks to build on last season's domestic double by regaining the Champions League crown from Real Madrid.
"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".
The match takes place tonight at 9pm in Tangier, Morocco, with this year's competition the first time the cup will be decided by a one-off tie as opposed to a two-legged affair.
In theory though, it is unlikely to be a major issue after Philippe Coutinho gained a Portuguese passport which takes him off the non-EU list.
Despite the adjustment potentially giving his side an edge, Barca boss Valverde is also far from content.
The Argentina global takes over from Iniesta following his move to Vissel Kobe in the J League at the end of the 2017-18 campaign.