The tie is delicately balanced at 0-0 after a stalemate in Manchester in the first leg on Tuesday.
Ronaldo has missed Real's last three matches, including Saturday's Gareth Bale-inspired 1-0 win over Real Sociedad, due to a thigh problem.
Ronaldo plays down injury concern
Benzema came off at half-time in the first leg suffering from a hamstring strain.
"In my head I hope and think that Cristiano and Karim will be fit and we will all be together," said Zidane.
The Frenchman made five changes from the side that started against City in San Sebastian as he also rested Toni Kroos, Marcelo, Pepe and Dani Carvajal.
Zidane emerges from Cruyff-tinged Clasico the winner
However, just as in last weekend's comeback from 2-0 down to win 3-2, Bale starred in the absence of Ronaldo and Benzema as his powerful header 10 minutes from time sealed Real's 10th consecutive La Liga win.
"I am happy for him because he has had problems this season with injury, but when is fit you notice," added Zidane
"We could have scored earlier in the first-half, but we had to work until the end against a difficult side.
"I am happy with the performance and to get three points once again."
Victory moved Madrid temporarily at least to the top of the table, but they later moved back to third place after Athletico Madrid and Barcelona won their respective matches.
"We have done our job, which is the most important thing," continued Zidane.
"What the others do we'll wait and see, but it doesn't matter. The most important thing was to win today ourselves.
"If we hadn't the league would have been a lot more difficult. Now we need to think about Wednesday."
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ