"(The players) all lost concentration, we weren't switched on for the free kick (that led to Sporting's second goal)".
Despite Lewandowski's return, Bayern have injury concerns of their own at the back. In fact, they've failed to win only once in their last 10 Champions League games - 2-2 at Borussia Dortmund in the group stage.
"We are not going to change the way we play, but Lewandowski is a player that scores a lot of goals and having him back gives us a lot of confidence".
Isco looks to be the best placed to step into Bale's boots in the Santiago Bernabeu Stadium after a wonderful display in Madrid's 3-2 win away to Sporting Gijon on Saturday, but the 24-year-old has played just 70 minutes in the Champions League this season. We're not at our best yet. We'll try to play our game and prepare well the game, like the first leg. This result is not definitive, so we need to play another great game. "At the end of the day, we're not so pessimistic".
With Gareth Bale ruled out with the calf problem he sustained in the first leg, Madrid will be relying on their star man.
Winning in Madrid is no easy task and even a 1-0 victory on Tuesday will not be enough after a 2-1 first-leg, quarterfinal loss in Munich.
"I hope he will be with us, but we have to wait and see", he added.
"We understand this is a very hard game, there's a ways to really go and Bayern are a very hard side. But we'll have a chance to win in Madrid".
Bayern badly missed their injured leading scorer last week, but now he's back and they must make the very most of his firepower by giving him plenty of ammunition.
Carlo Ancelotti: "Small details decided the first leg and we have to focus on those".
Zidane then suggested that he only replaced Bale as a precaution as he did not want to take any risk with the Wales global ahead of the coming crucial encounters with Bayern and Barcelona.
The striker should be joined by first choice defensive pair Mats Hummels and Jerome Boateng, but both face a race against time to be fit.
Ahead of Tuesday's second leg at the Bernabeu, Bale told Spanish outlet Mega: "I think we've been solid".
Bayern Munich conceded 12 shots on target in the first leg against Real, more than in any other Champions League game since Opta analysis began on the competition in 2003/04. Their two defeats during that time were against Barcelona in April 2011 (0-2) and Schalke in March 2015 (3-4). An early goal would give Bayern the flawless platform to take the game to Real, who are unbeaten in Europe's elite club competition this season.