Ronaldo has been allowed to leave the Portugal camp to begin a 10-day period of self-isolation.
The 35-year-old Juventus striker is currently asymptomatic and will miss Wednesday’s Nations League match against Sweden as a result.
All other members of Fernando Santos’ squad have tested negative for the virus.
The Portuguese Football Federation confirmed the news in an official statement on Tuesday, which reads: "Cristiano Ronaldo was released from training with the national team after a positive test for Covid-19, so he will not face Sweden.
"The Portugal international is doing well, without symptoms, and in isolation.
"Following the positive test, the remaining players underwent new tests on Tuesday morning, and all produced a negative result and are available to Fernando Santos for training this afternoon."
Ronaldo has played both games for Portugal during the international break, featuring for 72 minutes against Spain last week and playing full throttle in Sunday’s stalemate against world champions France.
Portugal are tied on seven points with France in their Nations League group.
Ronaldo will also miss Juventus’ Serie A game against Crotone over the weekend as well as the opening UEFA Champions League group stage game against Dynamo Kiev next week.
The former Manchester United and Real Madrid forward has scored three goals in two Serie A games this season.
