The Argentina international began court hearings on Friday, to answer allegations over unpaid tax on money from his image rights.
Messi has allegedly used countries outside of Spain - Belize and Uruguay - to sell his image rights, circumventing Spanish tax laws.
His father, Jorge, who made a payment of €5 million to the tax authorities in August, has also been implicated in the case and he too appeared in a separate hearing to his son.
Both men have strenuously denied the charges that date back to 2007 and 2009, which were originally levied against the pair by the Economic Crimes Prosecutor Barcelona in June.
And the pair's legal representative, Cristobal Martell, said Friday's proceedings are an opportunity for the Messi family to cooperate with Spanish authorities in an attempt to clear their name.
"To start a procedure like this we are following just one instruction: to cooperate with the administration to explain my client's actions and provide them with financial information," Martell commented.
"The instruction from the Messi family has been to be transparent, clear and cooperative.
"In terms of transparency, the hearings began today and we have provided evidence to show a complete unwillingness [by my client] to commit fraud, a strong effort to be transparent for the tax office and a desire to avoid entering into any kind of bitter fight with the State about these matters."