The seven-time World Champion has been left without a race-seat for next year's Championship after losing out to Lewis Hamilton.
Hamilton's replacement at McLaren has already been signed with Sergio Perez departing from Sauber and heading to Woking leaving the Swiss team with a seat open.
And that seat could yet go to Schumacher should the 43-year-old want to continue racing.
"Of course it's nice to think of such a possibility, that we can ask ourselves if we can get a seven-time World Champion when he is on the market," Kaltenborn told the Bild.
"Michael has until now been with just big stables which we can't compare ourselves to."
Team owner Peter Sauber has previously admitted an interest in Schumacher, saying he would "immediately" sign the German if he were available.