The Portuguese could have made his return in the midweek game against Barcelona, but the night before on Tuesday he tested positively again, leaving him with another anxious few days to see when he could be allowed to play.
On Friday evening, it was announced he was free of the virus, which means he'll go straight into the Juve squad for the Spezia match.
It is up to Andrea Pirlo as to whether Ronaldo actually starts on Sunday, but with the way Juve have been misfiring recently, he may opt to throw his star striker straight back in to the starting XI.
That could be at the expense of Alvaro Morata, who unfortunately saw three goals disallowed by VAR in Wednesday's 2-0 loss at home to Barcelona.
Another boost that the Bianconeri have received in the past few days is the return to full training of influential defender Giorgio Chiellini. He is available to start against Spezia, but with Juve expected to win that one comfortably, he may be rested for Champions League duty.
Federico Chiesa should return to the starting line-up after serving his one-match suspension against Crotone.