Lewandowski suffered a shoulder injury during last weekend's Bundesliga win over Borussia Dortmund, with Bayern complaining about his rough treatment, and lasted only 20 minutes of a training session this week as he fights to be fit.
Boss Carlo Ancelotti admitted in his Tuesday press conference that the Polish international was a doubt and that they wouldn't risk him.
"He has been training, just 20 minutes because he has problems with his shoulder, but we had a good feeling beforehand.
"We will finally decide whether he can play on Wednesday - if he is in pain, he won't play.
"I don't know if he will feel better (on Wednesday) but that will not change our idea or our strategy, nor our self-confidence. We know how important Lewandowski is, but we can be strong without him."
Ancelotti expects to be able to welcome back goalkeeper Manuel Neuer after his recent injury but defender Mats Hummels is definitely out after damaging ankle ligaments on Sunday.
Lewandowski's absence will be keenly felt, with the 28-year-old boasting 33 goals in 34 starts. Thomas Muller is expected to start in his stead.