According to Sport they want to pay 3 million, which is only 20% of his wages. I doubt there is anything there.
Was doing some digging, seems like Brazil maximum tax rate is around 27% which is around 18% less than Spain, as Brazilian resident he will be taxed on worldwide income, so whatever we pay him, it is taxed on Brazilian rules and not Spanish.
If they are ready to cover for his 20% net salary, that is more than 20% of his gross salary, in addition we save 18% of the rest of the salary we cover.
Too dizzy to do the math, but if this is correct there is big potential saving there while negotiating a deal with us.