The 33-year-old forward will miss the Selecao's friendly against Croatia on September 6 and the UEFA Nations League opener against Italy four days later.
Ronaldo, who joined Juventus from Real Madrid this summer, has only played in eight of Portugal's last 20 friendlies, though the Azzurri clash is a competitive fixture.
"After talking to the player, and after he moved to Juventus with all the processes of adaptation that entails, we understand it was best for him to not be present for these games," coach Fernando Santos told BBC Sport.
Ronaldo has won 154 caps for Portugal and scored 85 goals, including four in as many games at Russia 2018 on their run to the last 16.
Portugal squad in full:
Defenders: Joao Cancelo (Juventus), Ruben Dias (Benfica), Raphael Guerreiro (Borussia Dortmund), Pedro Mendes (Montpellier), Luis Neto (Zenit St Petersburg), Pepe (Besiktas), Mario Rui (Napoli), Cedric Soares (Southampton)
Midfielders: William Carvalho (Real Betis), Bruno Fernandes (Sporting Lisbon), Gedson Fernandes (Benfica), Ruben Neves (Wolverhampton Wanderers), Sergio Oliveira (Porto), Pizzi (Benfica), Renato Sanches (Bayern Munich)