The Real Betis full-back, who can play in several positions across defence and midfield, is suggested as a potential replacement for the outgoing Alberto Moreno.
Firpo is currently in action for Spain in the under-21 European Championships in Italy but remained tight-lipped when asked about rumours suggesting both Liverpool and Real Madrid were interested in his services.
"Did Madrid call me? If you want to know, you can ask them," the 22-year-old told El Larguero.
"I'm here with the national team and that's all I want to think about."
When asked about who he prefers out of Real and Barcelona by Marca earlier this month, Firpo added: "I have said that Real Madrid was more attractive to me because my father is from Madrid.