Prosecutors in Madrid have filed a complaint to a court in Pozuelo de Alarcon in which they accuse the Real Madrid star of a "voluntary" and "conscious" breach of his tax obligations.
Ronaldo is alleged to have created a "business structure" in 2010 to conceal his earnings from image rights between 2011 and 2014, according to a letter sent to the court by the prosecutor's office.
The Portugal captain, named by Forbes this month as the world's highest-paid athlete, is claimed to have defrauded the Public Treasury out of a total of €14,768,897.
The letter accused Ronaldo of: "Four crimes against the public treasury between 2011-14... which involves tax fraud of €14,768,897.
"The accused took advantage of a business structure created in 2010 to hide income generated in Spain from his image rights from tax authorities, which is a 'voluntary' and 'conscious' breach of his fiscal obligations in Spain."
Gestifute, the company owned by Ronaldo's agent Jorge Mendes, have so far been unavailable for comment.
Ronaldo moved to Madrid in 2009 after Manchester United accepted a then-world record transfer offer of £80m.
He has won 11 major trophies in his time in Spain, including a LaLiga and Champions League double in the 2016-17 season.
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