Cristiano Ronaldo has been left out of Juventus squad to face Empoli on Saturday with a muscular injury and is now a doubt for the Champions League quarterfinal against Ajax.

Ronaldo pulled up with an injury after 30 minutes into Portugal’s 1-1 draw with Serbia on Monday and will miss his third Serie A game in a row after being rested for the 4-1 win over Udinese and 2-0 defeat to Genoa.

“We need to be prudent,” Allegri told his prematch news conference on Friday. “It’s best if he misses one game rather than two months of the season. We’re heading into the final stages of the season and there’s not much time to recover, and we’ve still got two Champions League games to play.

“Ronaldo will return when there is no longer any risk of a setback. He’ll undergo tests on Monday and we’ll take it from there. Obviously he’s a doubt for the first leg, and Cristiano knows full well that if he’s not fit, he won’t play because we cannot risk the season in just one game.”

Juve, who lead Serie A by 15 points, travel to Cagliari on Tuesday before hosting AC Milan on April 6. Four days later, they travel to Amsterdam for the first leg of their quarter-final clash with Ajax.

In Ronaldo’s absence, 19-year-old Moise Kean is set to make only his second start for Juve, but Allegri said the Italy international — who opened his account for his country over the international break — also needs protecting, albeit in a different way.

“We need to take things slowly with Kean,” Allegri said. “He scored a goal against Liechtenstein, but with all due respect, people now want to liken him to (Lionel) Messi and Ronaldo.

“If [Italy coach Roberto Mancini plays him against stronger opponents in June and he doesn’t touch a ball, then everyone will be saying he’s rubbish. This isn’t on. We need to take things one step at a time. There’s no doubt there are times when he’ll score regularly, but to make out he is already a champion is taking it too far.

“We need to take things slowly. He needs to follow a normal pathway and I need to protect him.”