Arsenal right-back Bellerin earns a first call-up for four years after Sevilla captain Jesus Navas was substituted due to an injury at half-time during his club's 1-0 win over Osasuna.
Luis Enrique's side face a friendly against the Netherlands before Nations League matches against Switzerland and Germany.
Real Madrid attacker Asensio comes into the reckoning in place of Barcelona teenager Ansu Fati.
Like Navas, Fati only managed the first 45 matches of a LaLiga match at the weekend, making way for Lionel Messi in Barcelona's 5-2 triumph over Real Betis.
The Catalan giants later confirmed the forward has suffered a torn meniscus in his left knee, with a decision over treatment options to be made over the coming days.