Ronaldo, 33, last played for his nation at the World Cup in Russia, where they were eliminated by Uruguay in the round of 16.
Without him, Portugal have managed to reach the Nations League Finals, becoming the first side to qualify after Saturday's 0-0 draw with Italy in Milan.
But head coach Fernando Santos said there should be no questions that the Juventus star is still an important part of his squad.
"There is no doubt. If you still have doubts, I don't know," he told a news conference. But Cristiano Ronaldo is part of this team."
Ronaldo is Portugal's all-time leader in both goals (85) and appearances (154), while only Iran's Ali Daei (109) has netted more times in internationals