The 37-year-old has been sick to his stomach and missed a training session with the team.
Portugal announced that it will also keep Ronaldo out of the match against Nigeria in Lisbon on Thursday.
In recent days, a TV interview with Ronaldo has been the big topic of conversation in the football world.
The Portuguese superstar took the leaf out of his mouth and said among other things that he feels betrayed by Manchester United and that he does not respect the club's coach, Erik ten Hag.
Portugal kicks off the World Cup against Ghana on November 24.