The Portuguese attacker picked up a thigh injury in Saturday's 5-0 win over Almeria and was withdrawn nine minutes into the second half.
Ronaldo had scored his 25th goal of the season for Madrid in just the third minute, but will be unavailable for their UEFA Champions League clash against the Turkish side.
Carlo Ancelotti revealed Jese or Di Maria would be selected in Ronaldo's place and also confirmed Raphael Varane is unavailable for the meeting with Roberto Mancini's side.
The Italian said: "Cristiano won't play tomorrow because he has a small injury. We will need to wait and see if he can play on Saturday.
"Di Maria or Jese could replace Ronaldo. We have two options and I will decide tomorrow.
"Varane needs a break for his knee to recover well. He won't be available for 10 or 12 days.
"We won't risk and play Ronaldo on Saturday (against Real Valladolid) unless he is 100 per cent fit."
Ancelotti will also have to make do without the services of Fabio Coentrao (thigh), Sami Khedira (knee), and the suspended Luka Modric, while he also hinted Xabi Alonso could miss out after returning from injury only recently.
But the former Chelsea manager remains bullish about his side's chances as they chase a win that would confirm top spot in Group B.
He added: "The players know that it's difficult to choose a starting lineup. Rotations are made to keep everyone motivated.
"It's difficult to play 4-3-3 without Khedira but we will try to do it.
"The good thing is that we can play with different formations.
"We want to qualify as group leaders. It will be an intense match.
"(Roberto) Mancini has a lot of experience. He has done a great job in Italy and England where he won the Premier League.
"Galatasaray played well against Juventus. They are well-balanced and have dangerous players like (Didier) Drogba."
