The superstar's team, Juventus, made the announcement Friday ... saying the 35-year-old has finally tested negative after contracting the virus nearly three weeks ago.

"Cristiano Ronaldo carried out a check with a diagnostic test (swab) for Covid 19," the team said in a statement. "The exam provided a negative result."

"The player has, therefore, recovered after 19 days and is no longer subjected to home isolation."

It's great news for Juventus ... the squad won just 1 of its 4 games with Ronaldo out -- and lost its highly anticipated matchup with Lionel Messi's Barcelona team on Wednesday.

As we previously reported, it was announced on Oct. 13 that Ronaldo had COVID ... and he had quarantined himself every day since.

Though, based on his isolation pics, it didn't seem THAT difficult ...