The Portuguese striker has been accused by Spanish authorities of failing to pay 14.7 million euros (17.3 million dollars) in tax.
State prosecutors allege that Ronaldo siphoned money, earned from picture rights, past Spanish authorities between 2011 and 2014.
His lawyers have rejected the accusation, while the player himself says he has a clear conscience. Should he be convicted, he could be handed a jail term.
Ronaldo did not take part in a friendly match between his club Real Madrid and Barcelona in Miami, United States, on Saturday, ahead of the hearing in Pozuelo de Alarcon. Barcelona won the match 3-2.
The 32-year-old striker is not the only high profile football star to have been accused of tax fraud recently in Spain. Barcelona forward Lionel Messi was sentenced in May to 21 months in jail, though local media reported a month later that he is unlikely to serve time behind bars.
Manchester United manager Jose Mourinho also is accused of defrauding Spanish authorities to the tune of 3.3 million euros during 2011 and 2012, while coach of Real Madrid.