The 20-year-old product of the famed Barcelona youth system, who helped Spain's Under-21 team win the European championship last month, has had an impressive pre-season so far.
Thiago is also eligible to play for Brazil, with his father Mazinho being a member of the 1994 World Cup winning team.
"He [Thiago] is included for sporting reasons," Del Bosque told reporters in Madrid on Friday.
"He is a player who has been raised in Spain and who could choose to play for Brazil. But he has roots in Spanish football and this is just the next step."
Carles Puyol is injured while Joan Capdevila and Cesc Fabregas miss out for lack of match fitness with their clubs.
The world and European champions have five wins from five in qualifying for Euro 2012 and are six points clear at the top of Group I.
Their next opponents are Liechtenstein at home on September 6.
Goalkeepers: Iker Casillas (Real Madrid), Victor Valdes (Barcelona), Pepe Reina (Liverpool).
Defenders: Alvaro Arbeloa (Real Madrid), Sergio Ramos (Real Madrid), Raul Albiol (Real Madrid), Gerard Pique (Barcelona), Andoni Iraola (Athletic Bilbao).
Midfielders: Xabi Alonso (Real Madrid), Andres Iniesta (Barcelona), Sergio Busquets (Barcelona), Santi Cazorla (Malaga), Thiago Alcantara (Barcelona), Xavi (Barcelona), Javi Martinez (Athletic Bilbao).
Forwards: David Silva (Manchester City), David Villa (Barcelona), Pedro (Barcelona), Fernando Torres (Chelsea), Fernando Llorente (Athletic Bilbao), Alvaro Negredo (Sevilla), Juan Mata (Valencia).
