Prosecutors are claiming that the Brazilian left-back defrauded authorities of 490, 917 euros in 2013.
The accusations reportedly stem from Marcelo's use of companies abroad to handle earnings from image rights.
He joins a growing list of stars to be targeted by tax authorities in Spain. Lionel Messi, Cristiano Ronaldo, Ricardo Carvalho, Angel di Maria, Javier Mascherano, Radamel Falcao and Fabio Coentrao are among the other players who have been investigated.
Meanwhile, Marcelo's focus will solely be in the more immediate task at hand, Real Madrid's crunch clash with Tottenham at the Bernabeu on Tuesday evening.