De Gea has not played for United this season, due to widespread speculation that he may be on the move to Real Madrid before the transfer window closes on Tuesday.
But captain Iker Casillas is also in the Spanish squad, so De Gea may not see much action in these two qualifiers.
And Spain coach Vicente del Bosque says he is not yet too concerned about the 24-year-old’s lack of game time.
He said: “It’s true that he hasn’t been playing competitively, which normally is required, but we are also at the beginning of the season.
“He is active, he is training and, like others who are not necessarily first-choice with their teams, we think that at the moment he can come.
“If the situation drags on, then we might have to reconsider.”
Del Bosque also recalled De Gea’s fellow United player Juan Mata and Chelsea pair Diego Costa and Cesar Azpilicueta, who join team-mates Cesc Fabregas and Pedro in the 23-man squad.
Mata, Costa and Azpilicueta did not feature in Spain’s most recent qualifier, a 1-0 victory in Belarus in June.
Costa, who chose to play for Spain rather than his native Brazil, returns after a series of niggling injuries and Del Bosque said: “He is playing well and it appears he has put his problems behind him.
He is a player in whom we have a lot of confidence.”
After six matches, Spain are second in the group on 15 points, three behind leaders Slovakia, who defeated them 2-1 in Zilina in October.
The Spaniards are bidding for a third consecutive Euro title and they host Slovakia in Oviedo on September 5 before playing Macedonia in Skopje three days later.
Goalkeepers: Iker Casillas (Porto), David De Gea (Manchester United), Sergio Rico (Sevilla)
Defenders: Dani Carvajal (Real Madrid), Gerard Pique (Barcelona), Marc Bartra (Barcelona), Juanfran (Atletico Madrid), Sergio Ramos (Real Madrid), Jordi Alba (Barcelona), Juan Bernat (Bayern Munich), Cesar Azpilicueta (Chelsea)
Midfielders: Sergio Busquets (Barcelona), Koke (Atletico Madrid), Andres Iniesta (Barcelona), Santi Cazorla (Arsenal), David Silva (Manchester City), Vitolo (Sevilla), Isco (Real Madrid), Cesc Fabregas (Chelsea), Juan Mata (Manchester United)
Forwards: Diego Costa (Chelsea), Pedro (Chelsea), Paco Alcacer (Valencia)