The Welshman had to be withdrawn early in the first-leg in Munich, which Real won 2-1, after experiencing muscle tightness in his right leg and has not recovered in time to feature in the reverse fixture at the Santiago Bernabeu Stadium.
Madrid have not yet given a time-scale on his return but Zidane also admitted there is a strong possibility that he will also miss Sunday’s derby match against Barcelona.
“He will not play because we don't want to take any risks," Zidane said during his weekly press conference.
“He wants to come back, he has been working hard. Hopefully he will be back for the clásico but it's not certain yet. We will see how he progresses day by day.”
“Gareth has worked very hard to get back with the team after being out three months injured. When he returned he was very excited and happy. He has some issues which stop him being able to play. We just hope it is nothing serious.”
Sunday’s match between the fierce rivals will likely prove crucial in the title race, with the teams occupying first and second place in the Spanish league table.
Madrid, seeking its first league title since 2012, has a three-point lead and a game in hand, with six match-weeks remaining until the end of the season.
Zidane did not say who will replace Bale for the crunch match, but Isco — who scored twice to lead Madrid to a late 3-2 win over Sporting — is expected to start. Marco Asensio and Alvaro Morata are Zidane’s other attacking options.
“Isco is ready, like all of them,” Zidane said after the player had told reporters that he wants to remain at Real for ‘many years to come’.
“I have the decision made, but I will not tell you our plans, I'm sorry. Not about how we make the decision, or whether we will change the team shape.”
“We'll see how we will play, if we will change our scheme or not. I'm glad that everyone is prepared to play.”