Julen Lopetegui sprang a surprise by picking Arsenal's Nacho Monreal ahead of Chelsea's Marcos Alonso as the back up for Jordi Alba in his World Cup squad.
He gave a clue about that in an interview with Diario Spot, saying: "We have different ways of attacking and full-backs are important, but they need to be balanced, they should defend well too. Full-backs have to first defend and later attack."
The squad is:
Goalkeepers: David de Gea (Manchester United), Pepe Reina (Napoli), Kepa Arrizabalaga (Athletic Bilbao).
Defenders: Jordi Alba (Barcelona), Nacho Monreal (Arsenal), Alvaro Odriozola (Real Sociedad), Nacho Fernandez (Real Madrid), Dani Carvajal (Real Madrid), Gerard Pique (Barcelona), Sergio Ramos (Real Madrid), Cesar Azpilicueta (Chelsea).
Midfielders: Sergio Busquets (Barcelona), Isco (Real Madrid), Thiago Alcantara (Bayern Munich), David Silva (Manchester City), Andres Iniesta (Barcelona), Saul Niguez (Atletico Madrid), Koke (Atletico Madrid).
Forwards: Marco Asensio (Real Madrid), Iago Aspas (Celta Vigo), Diego Costa (Atletico Madrid), Rodrigo Moreno (Valencia), Lucas Vazquez (Real Madrid).