Ronaldo missed the weekend’s La Liga win over Rayo Vallecano with a thigh injury and did not feature in the goalless semi-final first leg at the Etihad on Tuesday night, despite training the day before.
Benzema, meanwhile, was withdrawn at half-time against City, leaving his participation for the return leg at the Bernabeu on May 4 in doubt.
“We hope that they can both be fit for the second leg, that’s the idea,” said Real head coach Zidane. “But we can’t say right now. We have to see. We have to take it day by day and see how they are.
“Cristiano felt something after that last training session. That’s why he didn’t play. Karim, it was a little bit different. But at the end of the day, little by little, he felt a little bit worse in himself. We don’t want to gamble with his fitness. We know how important both players are for us.”
Real had the better chances in a tight contest, with Benzema’s replacement Jese heading against the bar in the second half and Pepe firing a close-range shot at Joe Hart.
“I am happy with the game,” said Zidane. “It was not easy but in the end, we defended really well. We had the ball more in the second half and we had more chances after the break. It was a tough game but I am happy with the result.
“Before this game, it was 50:50 and now it’s the same. We have the second leg at home, but it’s 50:50. We are going to have to work like we did today.
“It is a Champions League semi-final so nothing is easy, but I am happy with the result and the work the players did.”
City did not have a shot on target until injury-time when Kevin De Bruyne’s free-kick needed to be tipped over by Keylor Navas.
“Defensively, we played really well,” said Zidane. “We know (Sergio) Aguero is a good player so we didn’t give him much space. The idea was to defend together. We managed to achieve what we wanted.”