The Portuguese scored in the 1-1 draw at the Johan Cruyff Arena last week, but was one of several players rested for Saturday’s defeat at SPAL.
“Cristiano has extraordinary quality,” said boss Massimiliano Allegri.
“In certain moments he becomes an unstoppable player and you can see it on his face.”
Fellow forward Mario Mandzukic will miss the game with a knee injury, with Allegri saying: “He has struggled to train at 100%. These games will be better suited to players who are in their best condition, because they have to give absolutely everything.”
Ajax’s biggest worry is about midfielder Frenkie de Jong, who hurt his hamstring in Saturday’s 6-2 win over Excelsior. Coach Erik ten Hag said they were confident he would be able to play.
“Frenkie himself will have to decide if he is ready, and eventually I decide if he will play,” said Ten Hag.
Ten Hag said he is optimistic his side can cause another upset, having beaten Real Madrid, European champions for the past three years, 4-1 at the Bernabeu in the last round.
“I’m confident because of the way we are playing and training. We are stronger and we are showing it game by game,” he said. “Juventus are the favourites, especially after the Amsterdam result.