Ronaldo is "well, without symptoms, and in isolation," the federation added.
The 35-year-old forward played for Portugal against France in the Nations League on Sunday and against Spain in a friendly last week.
Ronaldo will now miss his country's next Nations League match against Sweden on Wednesday, as well as Juventus' upcoming fixtures which include a Serie A match with Crotone and a Champions League group game against Dynamo Kyiv.