Cristiano Ronaldo ain't out of the woods yet ... he reportedly tested positive for COVID again, which means he won't be able to join his Juventus teammates to take on Barcelona next week.

Remember, the 35-year-old soccer superstar initially popped for COVID last week (it was announced Oct. 13) -- and was sent home from practicing with the Portugal national team.

CR7 has since been posting photos on social media showing him training and relaxing in his mansion -- with a big ol' smile on his face.