Prosecutors had earlier accused Uli Hoeness, 62, of evading a far smaller sum of 3.5 million euros in taxes and are seeking a jail term.
The former Germany forward kept the funds in a secret Swiss bank account.
He told the court he deeply regretted “my wrongdoing”.
“I will do everything necessary to ensure that this depressing chapter for me is closed,” Uli Hoeness said.
Uli Hoeness, who helped the national team win the 1972 European Championship and then the World Cup two years later, came clean about his secret bank account last year, filing an amended tax return in the hope of an amnesty in return for paying the tax he owed.
But prosecutors say he did so because investigators were already on his case.
The penalty for tax evasion can be 10 years in jail, though the prosecution says it will seek a seven-year sentence. A verdict is expected on Thursday.
Munich state prosecutor Achim von Engel read out the indictment against Uli Hoeness shortly after the start of the trial, described as one of the most spectacular of the year by the German newspaper Sueddeutsche Zeitung.
He alleged that the defendant had failed to declare the income he held at Vontobel bank in Switzerland.
Giving evidence later, Uli Hoeness said he had used the money for large-scale gambling on the foreign currency markets, losing far more than he ever gained.
“Between 2002 and 2006 I really gambled with sums that today I find difficult to grasp. For me it was a kick; pure adrenalin,” he said.
It was while Uli Hoeness was having lunch with Chancellor Angela Merkel on January 15 in Berlin last year that he was made aware of press interest in his finances, he told the court. Vontobel phoned him, he said. warning him that journalists from Stern magazine were making inquiries.
Before the scandal emerged, Uli Hoeness was considered to be on good terms with Angel Merkel, who has since said she is disappointed with him.
Uli Hoeness said he had already decided to come clean about his taxes to the authorities.
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