Rugani announced he had contracted the virus on Wednesday, 72 hours after he sat on the bench for Juventus’ win over Inter Milan.
The defender shared the same dressing room as Ronaldo and the rest of his teammates at the San Siro, where the game was played behind closed doors.
A statement from Juve read: “Juventus Football Club is currently activating all the isolation procedures required by law, including those who have had contact with him.”
Now all players from both teams have been forced to self-isolate.
Ronaldo is now in Madeira and is not allowed to return to Italy, the European country which is at present worst hit by Coronavirus with over 12,000 cases and a death toll of 827.