The 32-year-old, usually deadly in front of goal, hit the post twice against Alaves on Saturday afternoon as Los Blancos ran out 2-1 winners in the Basque Country.
Ronaldo squandered a glorious chance against Real Betis in Madrid's previous game, too, side-footing over the bar from close range when picked out by Gareth Bale in a match that his side would go on to lose.
Despite failing to find the net in La Liga since returning from a five-match ban, Zidane claims that the Portuguese will soon return to his best form.
"When you do not score, you are frustrated. But Ronaldo is calm," he told reporters. "He wants to score and he had the chances to do so. In the end, we always know he will make a difference eventually."
Ronaldo has attempted 18 shots without finding the back of the net in the Spanish top flight in 2017-18.