• Politician says Messi and his father badly advised on tax • They 'lack the financial knowhow' to have done this alone

A former Barcelona president, Joan Laporta, defended Lionel Messi against allegations of tax fraud on Thursday, a case that experts say could carry a prison sentence for the Argentina forward.

A Spanish state prosecutor filed a fraud complaint on Wednesday alleging that Messi and his father, Jorge, avoided paying €4m ($5.3m) in back taxes by illegally using overseas tax havens.

"I am convinced that neither Leo nor his father have committed any infraction," Laporta told Cope radio. "The situation could be that they don't have any responsibility in these events. There can be third parties who are responsible.

"I know them and they have always wanted to act within the law, and that's how they acted with the club, at least when I was president."

Laporta said that Messi and his family lacked the financial knowhow necessary to have set up the network of shell companies and tax havens in countries including Belize and Uruguay described in the prosecutor's complaint.

"They were always careful, let's say even wary, when faced with these situations that were over their heads because they didn't have the knowledge of a lawyer or a tax expert, and so they went out and got advisers," he said.

Messi has denied any wrongdoing and his lawyers issued a statement on Thursday saying that he "has always punctually attended to his fiscal obligations".

Spain's sports minister, Jose Wert, asked for "patience" given the long legal process that is likely to be ahead of the footballer. "(The law) is the same for everyone," he said. "Even for the No1."

The case was submitted at the court in Gavá, near the Mediterranean coastal town where Messi lives. A judge at the court must accept the prosecutor's complaint before charges can be brought against Messi and his father. A court official told the Associated Press that a decision should be made in a matter of days.

If found guilty and barring an out-of-court deal with the tax office, Messi and his father could face two to six years in jail, according to Professor Sandalio Gómez, a sports finance analyst at the IESE business school, University of Navarra.

Laporta, who was Barcelona's president from 2003-10 and is considering running again in 2016 after his foray into politics, said that under his mandate Messi directly controlled 100% of earnings from his image rights.

But, Laporta said, Barcelona did follow a common practice of paying 15% of Messi's salary to a company that controlled his image rights. He said that he didn't remember where that company was based.

"If it was a company based outside Spain it would have been a registered company and, in that sense, a lawful company," Laporta said.

Messi, who is rated by Forbes as the world's 10th highest-paid athlete, reportedly earned $41.3m to June this year, with $20.3m coming from his club salary and $21m in endorsements.