Portugal confirmed in a statement that Ronaldo is in isolation and not showing symptoms.
The statement added that following Ronaldo’s test, the remaining players in the Portugal squad underwent new tests on Tuesday, which came back negative.
Portugal will be without Ronaldo when they host Sweden on Wednesday in a UEFA Nations League game.
The 35-year-old played all of Sunday’s 0-0 draw against world champions France and Cristiano Ronaldo came closest to scoring when he fired a left-footed strike at goal in added time but his deflected shot was well saved by France goalkeeper Hugo Lloris.
Ronaldo is now a doubt for Juventus’ Serie A game against Crotone on Saturday and their Champions League opener against Dynamo Kiev next Tuesday as he undergoes an isolation period.
Last month, Ronaldo became the second male player to score 100 international goals as he scored twice in a 2-0 UEFA Nations League win against Sweden.
He is second in the all-time list of leading international scorers behind Iran’s Ali Daei, who scored 109 in his career.