The 27-year-old joined the Lisbon giants for the season last summer, having been strongly linked with the likes of Manchester United and Liverpool.
Now having impressed during his spell at the Estadio da Luz, reports in Spain claim that Real have decided to bring in Siqueira to compete with Marcelo - with Fabio Coentrao likely to depart.
But Granada have insisted that they have not agreed anything with their La Liga rivals, and insist that Benfica still have first option on him.
"There are clubs interested [in Guilherme Siqueira], but that doesn't matter. We have a big respect for Benfica at the moment," Granada president Enrique Pina told RAdio Renascenca.
"There is nothing signed with Granada or anybody. We respect Benfica and if they want [to sign him permanently], there isn't any problem."