The Poland hot-shot sat out Wednesday's 2-1 loss in Munich with a bruised shoulder.
The Poland hot-shot sat out Wednesday's 2-1 loss in Munich with a bruised shoulder as Cristiano Ronaldo chalked up his 100th European goal, scoring twice to cancel out Arturo Vidal's first-half opener.
"The medical department did a geat job trying to get him fit, but the risk was too great," Rummenigge said after the defeat.
"For the return leg, he will be 100 percent ready."
Despite Rummenigge's optimism, Bayern coach Carlo Ancelotti was more cautious, hoping both Lewandowski and defender Mats Hummels, who missed the home defeat with an ankle injury, will be fit for the return.
"We have six days, it is possible they will both be fit," said the Italian.
Lewandowski has scored 38 goals in all competitions this season, including seven in the Champions League, and Bayern missed his finishing at the Allianz Arena.
He netted twice in last Saturday's 4-1 win at home to Borussia Dortmund in the Bundesliga, but injured his right shoulder in a collision with the visitors' goalkeeper Roman Burki.
He initially declared himself fit to face Real, but managed only 20 minutes of Tuesday's final training session.
After five yellow cards this season in the Bundesliga, Lewandowski has extra time to recover as he is suspended for Saturday's league clash at Bayer Leverkusen.