"Monreal comes from the Under-21s, he has been in the Primera Liga for four years and has played many games. He has a lot of experience despite his youth," Del Bosque told a news conference.
"It would be nice to call up more players for the future, like we have with Monreal, but we have to keep focused on the present."
Real Madrid defender Sergio Ramos was unavailable because of tendinitis, while Barcelona midfielder Andres Iniesta and Villarreal midfielder Marcos Senna are not back to match fitness after long-term injuries.
Two fringe players who missed out after playing in South Africa were Athletic Bilbao striker Fernando Llorente and Valencia midfielder Pablo Hernandez, though Del Bosque praised the contributions both made.
The European champions came third in the Confederations Cup after a shock 2-0 semi-final defeat to the United States, but are on course to qualify for the 2010 World Cup as they top Group Five with a 100 percent record from six matches.
They lead second-placed Bosnia by six points and host Belgium and Estonia in their next qualifiers on Sept 5 and 9.
"The Confederations Cup was a positive experience overall," Del Bosque added.
"We weren't able to get to the final as football is full of surprises but I prefer to look at the year as a whole when 14 of our 15 games went our way.
"We are on course for our main objective which is to qualify for the World Cup finals, but we must remain vigilant."
The squad will gather in Madrid on Monday and fly to Macedonia the following day for the Aug. 12 match.
Squad:
Goalkeepers: Iker Casillas (Real Madrid), Pepe Reina (Liverpool), Diego Lopez (Villarreal).
Defenders: Raul Albiol (Real Madrid), Alvaro Arbeloa (Real Madrid), Joan Capdevila (Villarreal), Carlos Marchena (Valencia), Gerard Pique (Barcelona), Carles Puyol (Barcelona), Nacho Monreal (Osasuna).
Midfielders: Xabi Alonso (Real Madrid), Sergio Busquets (Barcelona), Santi Cazorla (Villarreal), Cesc Fabregas (Arsenal), Xavi (Barcelona), David Silva (Valencia), Juan Mata (Valencia), Albert Riera (Liverpool).
Forwards: David Villa (Valencia), Daniel Guiza (Fenerbahce), Fernando Torres (Liverpool).
