Ronaldo has scored two goals in 10 league games and came in for criticism in the Spanish media for his display in Real's goalless draw against Athletic Bilbao last weekend which left the Liga champions eight points behind leaders Barcelona.
The 32-year-old is still expected to pick up the Ballon d'Or award on Friday (NZ time) for firing Real to Champions League glory last season, scoring hat-tricks against Bayern Munich and Atletico Madrid in the quarter and semifinals and a double in the 4-1 win over Juventus in the final.
If he wins the award, Ronaldo will tie Lionel Messi's record of being named the best player in the world five times.
"I think Cristiano deserves more respect because he is such a great player that when things don't quite go his way everyone has something to say about him," Zidane told a news conference ahead of Real's final Champions’ League Group H game with Borussia Dortmund.
"The club and the fans who love Cristiano Ronaldo know what he is doing. Just last season he had a phenomenal campaign. We are halfway into the season; we still have six months left of the season. Six months is a very long time for Cristiano."
Ronaldo has lived up to his high standards in the Champions League in which he is the top scorer with eight goals from five games and on course to become the top marskman in Europe's elite competition for a sixth straight year.
"For me he deserves to win the Ballon d'Or because he's had an incredible year," Real midfielder Mateo Kovacic said.
"I'm very happy for him, the Ballon d'Or means a lot to him and to us although the most important thing is that we win together as a team.
"I see Cristiano train every day and he is doing fine. He's going to score a lot of goals this season. Right now the ball doesn't want to go in for him, but there's a long way to go and he's going to start scoring again."
Real are guaranteed to finish second in Group H behind Tottenham Hotspur.
Photo by: JAVIER BARBANCHO/REUTERS. Caption: Cristiano Ronaldo is on course to win a record-equalling five Ballon d'Or awards, but has been criticised for his quiet time of it in La Liga.