The goalkeeper has been overlooked by a coach he worked with previously at Porto, while the Chelsea midfielder's difficult spell goes on
The veteran goalkeeper and Chelsea midfielder have been dropped for the friendly with Belgium and the World Cup qualifier against Liechtenstein next month.
Atletico Madrid youngster Saul Niguez has been handed a place, while there are recalls for striker Diego Costa, Manchester United playmaker Juan Mata and Bayern Munich's Javi Martinez.
Andres Iniesta has been left out as he continues his recovery from a knee injury, while Isco was omitted at the last moment after taking a knock in training, Lopetegui has said.
West Ham's Adrian has been drafted in to replace Casillas, but Lopetegui insists the Porto goalkeeper's international career is not over.
"The conversation with Iker was sincere, between friends," he said. "It was done eye-to-eye and we said what we thought.
"I understand the questions, it's logical. Iker will continue to be very close to us.
"Everyone knows the world of football and we know that nothing is definitive."
He continued: "All the players who are coming into this squad have been directly analysed.
"There is no kind of interference in the list. My only interest is football.
"It will be a pleasure to work with Pepe Reina and Adrian. I've always liked to do so with De Gea.
"Sergi Roberto for Juanfran? Juanfran is an excellent player and he's done very good work here, but in this case I've decided to choose Sergi because he's adapted really well to full-back and he is more multi-purpose."
Squad in full:
Goalkeepers: David de Gea (Manchester United), Pepe Reina (Napoli), Adrian (West Ham)
Defenders: Dani Carvajal (Real Madrid), Gerard Pique, Sergi Roberto (Barcelona), Javi Martinez (Bayern Munich), Sergio Ramos (Real Madrid), Marc Bartra (Borussia Dortmund), Jordi Alba (Barcelona), Cesar Azpilicueta (Chelsea)
Midfielders: Sergio Busquets (Barcelona), Saul Niguez, Koke (Atletico Madrid), David Silva (Manchester City), Thiago (Bayern Munich), Juan Mat (Spain).
Forwards: Alvaro Morata (Juventus), Vitolo (Sevilla), Lucas Vazquez (Real Madrid), Nolito (Manchester City), Marco Asensio (Real Madrid), Diego Costa (Chelsea), Paco Alcacer (Valencia