Mascarell mainly represented Madrid's B and C teams during his time at the Bernabeu, but the defensive midfielder did make one La Liga appearance for the Spanish giants in June 2013.
The 25-year-old was sold to Frankfurt at the end of the 2015-16 campaign, but it is understood that Los Blancos have a buy-back clause.
According to Marca, Madrid are interested in paying the £3.5m transfer figure to bring the former Spain Under-20 international back to the Bernabeu with the view to a potential first-team position.
The same report also claims that the Spanish club could re-sign the midfielder before selling him for a higher transfer figure.
Mascarell has previously spent time on loan at Derby County and Sporting Gijon.