Ronaldo, 35, was sent home from Portugal’s training camp last Tuesday after returning his first positive coronavirus test while on international duty with Fernando Santos’ men.
The former Real Madrid man returned to Turin to undergo a self-isolation period of 14 days, but Portuguese outlet Correio da Manha claim he has returned another positive reading after taking a second test.
That means he is now highly unlikely to be involved in Juve’s crunch Champions League clash with Barcelona next Wednesday.
UEFA protocol states that a player must return a negative test one week before every match, which Ronaldo has not been able to do.
As a result, the Ballon d’Or legend will have to watch from home as Andrea Pirlo’s men go head-to-head with Messi and co at the Juventus Stadium.
Nevertheless, he could line up against his arch-rival at the Nou Camp on December 8 if both men are in good health by then, which would be the first time they have ever locked horns in the Champions League group stages.
The iconic duo have met on three separate occasions in the knockout rounds, with Ronaldo’s Manchester United winning one semi-final tie against Barca in the 2007/08 campaign.
Messi and the Catalans came out on top in the final against United the following year, before they picked up a crucial victory over Ronaldo and El Clasico rivals Real Madrid in 2010/11.
It is unclear when Ronaldo will be back in action, as he is now likely to undergo another isolation period of at least another 10 days.
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Despite his latest positive test, the forward appears in good spirits after taking to Twitter on Thursday to show off his new shaven haircut.
He has also been making sure he stays in solid physical condition while in quarantine, having been spotted working out on an exercise bike on social media.