The 27-year-old is currently on loan at Benfica, whom he joined from Granada at the start of the season.
A recent report had claimed that Los Blancos had secured the signing of the left-back for next season, but Pina has quelled such suggestions.
"There are clubs interested [in Guilherme Siqueira], but that doesn't matter. We have a big respect for Benfica at the moment," 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."
A number of European clubs are believed to be monitoring proceedings.