Law firm Juarez Veciana said in a statement that the Barcelona forward "scrupulously complies with Spanish legislation."
Messi and his father Jorge have been ordered to appear before court in the town of Gava near Barcelona on Sept. 17 to answer allegations they owe 4 million euros ($5.3 million) in back taxes from 2007 to 2009.
"We declare that our client will pay the amount determined," Messi's lawyers said. "But we believe that our client has already paid what was legally obliged."
The state prosecutor alleges Messi and his father used shell companies in Belize and Uruguay to avoid paying taxes on revenues from image rights.
The complaint lists Messi's sponsors from the period under investigation. They include Barcelona, Adidas, Danone, Konami, Procter & Gamble, Pepsi-Cola and Telefonica, among several others.
If charged and found guilty — and barring an out-of-court deal — Messi and his father could face a fine amounting to 150 per cent of the concealed earnings and between two and six years in prison.
Messi, whose quiet life has until now kept him clear of any scandal, has denied any wrongdoing. He has received public backing from Barcelona club president Sandro Rosell and predecessor Joan Laporta, who was in charge during the years of the allegations.
The 25-year-old Messi is widely considered the best player of his generation after winning an unprecedented four straight FIFA world player of the year awards. He scored 60 goals in the Spanish league this season to lead Barcelona to its fourth domestic title in five seasons.
He is rated by Forbes as the world's 10th highest-paid athlete after reportedly earning $41.3 million to June this year, with $20.3 million coming from his club salary and $21 million in endorsements.
Messi's court date may clash with Barcelona's opening game in the Champions League next season, to be played on either Sept. 17 or 18.