Real Madrid coach Zinedine Zidane has confirmed that Gareth Bale will miss Tuesday's Champions League quarterfinal second leg against Bayern Munich through injury, and said he is also a doubt for Sunday's Clasico against Barcelona.

Bale picked up his latest calf muscle problem in Wednesday's 2-1 first leg win in Germany, and although Madrid have not confirmed the extent of the problem, he has not trained with his teammates since and missed Saturday's 3-2 La Liga victory at Sporting Gijon.

Asked for an update on Bale's fitness at the pregame news conference before the second leg against Bayern, Zidane said that he could not be sure how much longer the 27-year-old would be missing.

"Gareth has worked very hard to get back with the team after being out three months injured," Zidane said. "When he returned he was very excited and happy. He has some issues which stop him being able to play. We hope it is nothing serious, and he is back with us shortly.

"He deserves to be with us for this end to the season. Tomorrow he won't be there, we don't want to take any risks. I hope he can be with us [for the Clasico] but I cannot be sure. We go day by day."

Isco stood out with two goals including a last-gasp winner in Saturday's game, but he has been used sparingly in Europe this season, getting just 77 minutes in total across Madrid's nine Champions League games to date.

Zidane would not say whether Isco, or other options including James Rodriguez, Marco Asensio or Lucas Vazquez, would deputise for Bale against Bayern.

Isco has not been a regular for Real Madrid in the Champions League this term. MIGUEL RIOPA/AFP/Getty Images

"That Isco has not played much time in the Champions League is just coincidence, there is nothing else," Zidane said. "It looks tough for him, just 77 minutes, it's not much. But we have many games, many competitions, and we will see tomorrow what will happen.

"Isco is ready, like all of them. 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."

A Cristiano Ronaldo double helped Madrid turn around the first leg in Bayern, after the German side had the better of the first half and could have been 2-0 up but for a missed Arturo Vidal penalty.

Zidane said that even with the advantage his team now held, they would not be taking anything for granted, and the inclusion of Bayern's fit again centre-forward Robert Lewandowski would not change his thinking.

"We must go out to win the game, not think about protecting our advantage or anything else," he said. "The first leg is already over.

"We know how difficult it will be. Bayern play the same at home or away. We know Lewandowski is a real No. 9, the player he is. It is a plus for Bayern, but I am not concerned about that, they have good players in every position. We must focus above all on what we can do ourselves. We know they have a lot of options to damage their opposition, and like all teams they have their defects. So we will prepare well for the game, as we did for the first leg. We know that we must play another great game."

Asked to confirm a Marca story on Monday morning that Real president Florentino Perez had assured Zidane that he would stay in the job next season regardless of how results went between now and June, he said: "[I know] nothing about that. I just live day to day."