Spanish tax authorities launched a formal complaint against the Real Madrid forward last month, accusing him of hiding revenues generated from his image rights.
The Portuguese footballer was heard for 90 minutes at a court in the Madrid suburb of Pozuelo de Alarcón on Monday morning.
He said he would give a statement to the media after the hearing, but then left the court via the back door without appearing in public.
Ronaldo had previously said his conscience was clear, and Gestifute, the agency that represents Ronaldo which is owned by the businessman and agent Jorge Mendes, said at the time of the launch of the probe that that Ronaldo “never had a tax problem, contrary to what the Spanish prosecutors insinuate”.
Later on Monday, Ronaldo said in a statement, “The Spanish Treasury knows in detail all my income, because we have given them, I have never concealed anything, nor did I intend to evade taxes.
"I always do my tax returns voluntarily, because I think we all have to declare and pay taxes according to our income.
"Those who know me know what I ask my advisors: to have everything up to date and properly paid, because I do not want problems.
"When I signed for Real Madrid, I did not create a special structure to manage my image rights, but I kept the one that managed them when I was in England."
He added, “Now it is time to let the justice system do its work. I believe in justice and I hope that, in this case as well, there is a just decision. And in order to avoid any unnecessary pressure or contributing to any kind of parallel trial, I have made the decision that I will not comment further about this issue until that decision is made."
Following today’s hearing, the judge will decide if there are grounds to charge him. If he is found guilty, Ronaldo could face a prison sentence of between one and five years.
Prosecutors alleged that he entered into a “business structure” in 2010 in a “conscious” and “voluntary” way with the intention of not declaring income. As a result, he was charged with four offences which allegedly took place between 2011 and 2014.
But Gestifute said Ronaldo used the same structure he had in the UK, when he was playing for Manchester United between 2003 and 2009.
Gestifute said Ronaldo’s structure used to pay his image rights taxes was “perfectly legal”, since it was recognised and validated by the UK Treasury.
The agency pointed out the structure is usual among players in England with, it claimed, around 180 players currently operating one.
Back in May, the Spanish Supreme Court confirmed the 21-month jail sentence handed to the Barcelona striker Lionel Messi last year.
Messi and his father were both sentenced in July last year after being found guilty of three counts of tax fraud.
The footballer was sentenced to 21 months in prison and fined €2m. Jorge was also handed a 21-month sentence at the time and fined around €1.5m, but his sentence was reduced to 15 months after he paid some of the taxes.