The Economic Crime Section of the Provincial Prosecutor's Office of Madrid has filed a complaint with the Court of Instruction.
Jose Mourinho's representatives have insisted that they have not been contacted by the Spanish tax authorities regarding allegations of fraud.
They also circulated a copy of a tax document dated July 3, 2015, which covers the period in question.
The Portuguese football star is set to take on Russian Federation as it hosts the 2017 FIFA Confederations Cup on Wednesday, but his mind might be on being called to testifty before a Spanish judge on July 31st.
Ronaldo and Mourinho are both clients of agent Jorge Mendes.
A prosecutor said that Mourinho did not declare income from use of his image rights in order to gain an "illicit benefit". In 2010, the law was altered so that anyone earning more than 600,000 euros annually would not be eligible, and Spanish prosecutors have since taken a closer look at the taxes paid by wealthy foreigners.
According to Marca, Mourinho doesn't want Ronaldo, with suggestions that their patchy previous relationship or a distrust from the manager on the player's motivation to leave Real put down as possible reasons by the Spanish publication.
The football world in Spain has been rocked by charges of tax evasion or corruption pressed against some of its top stars.
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