Manchester City's Rodri, a key player for his country, suffered a severe knee injury in September and will be out for the rest of the season.
Rodri was vital in holding midfield as Spain clinched Euro 2024 victory this summer but Real Sociedad midfielder Zubimendi, 25, also made a big impact in the final.
Zubimendi replaced the injured Rodri at half-time against England in the Berlin final as La Roja triumphed 2-1 with two goals after the break.
"Zubimendi has been playing (brilliant) games for a long time, if Rodri is the best player then Zubimendi is the second best in this position," De la Fuente told a news conference.
"He's got experience under his belt, he oozes security through every pore of his skin.
"Martin doesn't get nervous... he's a very mature player, so calm... Zubi is a sure bet, who never fails."
Nations League champions Spain, second in group A4, host leaders Denmark on Saturday in Murcia, before welcoming Serbia to Cordoba on Tuesday.
They are also without Real Madrid right-back Dani Carvajal, who is also set to miss the season with a knee injury, and explosive winger Nico Williams with a minor knock, among others.
"We're not going to cry, we're not going to make excuses about missing players, the ones who are here are very good too, also the best (players in the world) for me," continued the coach.
"Whoever is playing tomorrow in the place of Nico, or Rodri, or Dani, are absolutely great... they will give us more tactical richness.
"We're not going to change anything in terms of our plan or our idea of football... the idea is very clear."
De la Fuente said injuries were the "ugliest" part of football, but they also created opportunities.
"Nobody is irreplacable... those who get the chance, albeit for unfortunate reasons, it's the time to take advantage of it," added De la Fuente.
