But following the revelations Ronaldo is ready to leave Madrid over his allegations of tax fraud in Spain, a return to United has been mooted.
Manchester United manager Jose Mourinho was on Tuesday accused of evading €3.3 million (Dh13.5m) in tax at Real Madrid, the public prosecutor's office in Madrid announced.
Spanish prosecutors filed a claim against the former Real manager on counts of fraud dating from 2011 and 2012, Reuters reported on Tuesday.
The frenzy of speculation began soon after Ronaldo was accused last week of a 14.7 million euro ($16.8 million) tax evasion through offshore companies.
It will now be up to a judge to decide whether to take the matter to court.
In addition, they say he only declared 11.5 million euros of Spanish-related income from 2011 to 2014, while what he really earned during that time was close to 43 million euros.
But tax authorities later found that some of the information presented in that settlement was incorrect, the prosecutors said.
In the season just ended, he won three trophies in his debut campaign at Manchester United, although he drew criticism after a poor league performance.
Other big names in football have been accused of tax fraud in Spain recently.