The 31-year-old is alleged to have directed at least €150m (£127m) of his income through tax havens since joining Real Madrid from Manchester United in 2009.
Ronaldo’s agency Gestifute has strongly denied the claims, but Jose Maria Mollinedo – the secretary general of the union at Spain’s tax authority (GESTHA) – revealed that if found guilty the three-time Ballon d’Or winner could face jail.
“The information about Cristiano Ronaldo makes it look like he could have defrauded more than €150m,” Mollinedo told Spanish radio station RAC1.
“We’d be looking at a major fiscal crime. This would fit a minimum prison sentence for each tax year of the fraud. If the open inspection is for three years, [then it would be] a minimum of six years in prison.
“If, before two months have passed from the opening of the investigation, they legally recognise the facts and pay back the defrauded amount, the punishment can be reduced.”
Manchester United manager Jose Mourinho is also alleged to have been involved in tax evasion.