A reported target of Arsenal and Liverpool, the 24-year's only previous appearance was as a substitute in the January friendly against Colombia, when coach Tite picked only home-based players.
"He is a player that had a great Olympics and he was always on our radar," Tite said of Luan, whose midfield promptings helped Brazil win the Olympic soccer gold last year for the first time. "He is a principal link up player and deserves to be called up."
Corinthians goalkeeper Cassio was the other surprise inclusion.
The big keeper has been outstanding in the Corinthians' rise to the top of the league and is well-known to Tite from when he led the Sao Paulo side to the Copa Libertadores in 2012.
Top of the South American table, Brazil have already qualified for Russia 2018 and have won all eight of their qualifiers since Tite took over in the middle of last year.
They play Ecuador at home on Aug 31 before flying to Colombia to face the home side on September 5.
The top four in the South American section qualify automatically for Russia. The fifth-place side goes into a play-off with a team from the Oceania confederation.
GOALKEEPERS
Alisson (Roma), Cassio (Corinthians), Ederson (Manchester City)
DEFENDERS
Dani Alves (PSG), Fagner (Corinthians), Filipe Luis (Athletico Madrid), Marcelo (Real Madrid), Marquinhos (PSG), Miranda (Inter Milan), Rodrigo Caio (Sao Paulo), Thiago Silva (PSG)
MIDFIELDERS
Casemiro (Real Madrid), Fernandinho (Manchester City), Giuliano (Zenit), Luan (Gremio), Paulinho (Guangzhou Evergrande), Philippe Coutinho (Liverpool), Renato Augusto (Beijing Guoan), Willian (Chelsea)
FORWARDS
Firmino (Liverpool), Gabriel Jesus (Manchester City), Neymar Jr (PSG), Taison (Shakhtar Donetsk)
(Writing by Andrew Downie, Reporting by Rodrigo Viga Gaier, editing by Larry King)
