Lewandowski suffered a broken jaw, a broken nose and a concussion when he collided with Borussia Dortmund goalkeeper Mitch Langerak in their DFB-Pokal defeat on Tuesday.
When asked if Lewandowski will be fit to face Barcelona on May 7, Rummenigge told B5 Aktuell: "That will be the case – I am pretty convinced of it. He will have an individual mask made and that should ensure he will play against Barcelona."
Ribery meanwhile has been recovering from an ankle injury and has not played since Bayern thrashed Shakhtar Donetsk 7-0 in the Champions League in mid-March.
However, Rummenigge pointed out that he is confident Ribery will be included in the squad since the team's medical staff are "working day and night" to ensure he becomes fully fit as soon as possible.
"Our hope is that he can at least make the squad on Wednesday," Rummenigge said. "Our doctors are working day and night to make this possible."