The Argentina star and his father Jorge Horacio Messi have been accused of using companies in Belize and Uruguay to avoid paying taxes on €4.16 million ($4.6 million) of Messi's income earned from his image rights from 2007-09.
Barcelona forward Messi's defence lawyers want both the five-time World Player of the Year and his father to be absolved.
But the state attorney - who in Spain intervenes in trials in parallel with prosecutors when the interests of a public organisation have been impacted, in this case the tax authorities - wants both sentenced.
"Lionel Andres Messi must be absolved," Prosecutor Raquel Amado said in her closing argument, a day after the footballer took the stand and said he trusted his father with his finances and "knew nothing" about how his wealth was managed.
"There is no evidence that anyone explained anything to him."
But she maintained her accusation against his father, for whom she asked for a jail sentence of one-and-a-half years.
Any such sentence would likely be suspended as is common in Spain for first offences carrying a sentence of less than two years.
"It's because Jorge Messi accepted it that this happened," she said.
The income related to Messi's image rights that was allegedly hidden includes endorsement deals with Banco Sabadell, Danone, Adidas, Pepsi-Cola, Procter & Gamble and the Kuwait Food Company.
"These contracts are in English, most certainly bulky," Amado argued.
"For a layperson, if they see so many lawyers signing it, they must believe that it's fine."
The companies in Uruguay - which much of the probe centres on - were created and managed by a Barcelona law firm with whom Messi's dad communicated.
"Mr. Jorge Messi cannot dodge his responsibility by accusing his advisors," she said.
"Fraud takes place because there is a decision in that direction."
Messi and his father did not attend the fourth and final day of the trial, in which defence lawyers and the state attorney have yet to make their closing arguments.
The player had been due to jet off to the United States after his Thursday court appearance for the Copa America where Argentina take on defending champions Chile on Monday.
No date has been set for when the court will issue its ruling.