So my take on this would be if existing laws were broken, or fraud was committed then everybody involved should be punished/fined etc.... But it does look like Ronaldo has a case for the defense. From my understanding, Ronaldo was taking advantage of the Beckham Tax Law in Spain. Which gives a reduced rate of 24% on the first €600,000 earned. Here is the best part, under the Beckham Law, any income outside of Spain remains tax-free, providing that tax is paid in the jurisdiction where the earnings are made.
If you bring the money onshore you could get hit with a tax of 52%. But you can only take advantage of the Beckham Law for 6 years. Since 2015 Ronaldo's eligibility for this law expired, but on the 1st January 2015, the law was reformed and excluded athletes from the scheme
From an old article in The Guardian: " from 2011 to 2014 he defrauded the Spanish treasury of €14.7m in taxes." and "It is alleged that he concealed income from the sale of image rights through a financial structure that diverted the money via Ireland to a tax haven in the British Virgin Islands."
The tax structure Ronaldo has is very popular with Multi-National Corporations. For example, GOOGLE HQ in Ireland pays a large tax-free royalty each year to GOOGLE in the Burmuda for use of their software products.
So the situation is not very clear, seems like Ronaldo did everything by the book, except the British Virgin Island tax haven scheme. But even then the Spanish Authority has no right to any income earned for Ronaldo's image rights until 2015, which were earned outside of Spain.
Also this new figure of €28m, I'm not sure but that seems excessive.
Forbes: "The claimed reporting shortfall of €31.5m translates into additional tax due of €14.7m ($17m) but when interest, fines, and costs are added the tax authority wants Ronaldo to pay €28m ($32.5m)."
This is a 50% tax rate (€14.7m) on image rights, with €13.3m in fines and interest. Seems extortionate at this rate.