The four-day trial of Uli Hoeness (pictured, second from right) began with a surprise confession.

The president and supervisory board chairman of football club Bayern Munich admitted on Monday that he had failed to pay a total of 18.5 million euros ($25,7 million) - 15 million euros more than he stands accused of.

"I evaded taxes," Hoeness said. "Now I want to come clean." He went on to stress that he was not a freeloader, but that he had made donations to the tune of five million euros and had paid 50 million euros in taxes over the past few years.

According to the prosecution, Hoeness held two bank accounts in Switzerland, which he used for extensive speculation on the stock and currency markets. He failed to declare earnings and is now charged of failing to pay 3.5 milllion in taxes from 2003 to 2009; he also stands accused of wrongly declaring losses to the tune of 5.5 million.

Hoeness told the court that he had simply lost track of his dealings.

In January 2013, he filed an amended tax return in which he voluntarily disclosed some of his dealings. Under German law, such a comprehensive amended tax return filed before prosecution sets in, can protect the offender from a jail sentence.

However prosecutors argue that Hoeness' disclosure was incomplete. He could face up to 14 years in jail, if held fully responsible.

To stall an arrest warrant and avoid a jail sentence, Hoeness has already paid 10 million euros in bail.

The 62-year-old former German national team player rode to the court house in Munich on Monday in a limousine with blacked-out windows. He was accompanied by his wife Susi and ushered past several critics and supporters.

Judge Rupert Heindl adopted a tough stance and asked Hoeness repeatedly for details of his actions, which saw the Bayern president increasingly flustered as proceedings continued throughout the day.

Public interest in the trial is huge. The case has triggered a heated debate in Germany about whether tax evaders who confess should be allowed to get off free, and whether celebrities were given special, lenient treatment.

Bayern Munich and its fans have stood by Hoeness, who led the club to international success, rejecting his offer to suspend his club duties.

But Hoeness, who also runs a successful sausage factory in Nürnberg and is one of Germany's top businessmen, has lost his standing as moral authority.