Other clients of Mendes who have ended up in Spain include the Portuguese full-back Fabio Coentrao - on the verge of joining Sporting Lisbon on loan from Real Madrid - and Colombian striker Radamel Falcao, now with Monaco but formerly at Atletico Madrid.
Last week, Ronaldo was accused by a state prosecutor of four counts of tax fraud totaling 14.7 million euros ($16.5 million). This is similar to deals struck with the Spanish taxman by his fellow Argentinians Javier Mascherano and Lionel Messi a year ago.
Representatives for Ronaldo declined to comment. A judge will then decide if they are grounds to charge him with a crime.
The Spanish tax authority claims that between 2011 and 2012 Mourinho did not pay €3.3m (£2.9m) in due taxes.
He has gone on to deny any wrongdoing, and went on to detail what he spent on taxes during his time living in Spain between 2010 and 2013.
The claim, which dates to a period between 2011 and 2012, alleges that money due from the use of his image rights were steered into 'corporate structures [which] were used by the accused in order to hide revenues'.
A prosecutor said that Mourinho did not declare income from use of his image rights in order to gain an "illicit benefit". The Madrid prosecutor said the case was presented to a local court.
The Argentinian, who now plays for Paris Saint-German, is unlikely to spend any time behind bars though - most sentences under two years in Spain are suspended for first-time offenders.
Last year, Messi and his father, Jorge Horacio Messi, were found guilty on three counts of defrauding tax authorities of 4.1 million euros ($4.6 million) from income made from image rights.