The superstar hit the post in the second leg clash against AC Milan with the aggregate score at 1-1.
Fans were quick to take to social media and say Ronaldo was copying his Barcelona rival Lionel Messi in missing the penalty.
Meanwhile, Juve are missing captain Giorgio Chiellini, striker Gonzalo Higuain, Wales midfielder Aaron Ramsey and Turkey defender Merih Demiral.
On the other hand, Milan are without injured Zlatan Ibrahimovic as they attempt to beat Juve in Turin for the first time since 2011. Forward Samu Castillejo and defender Theo Hernandez are suspended.