The Bundesliga outfit are missing key first-team stars Jefferson Farfan and Klass-Jan Huntelaar, who is out for the rest of the calendar year.
Schalke lead the group on six points, with Chelsea second on three, and Keller says he would be satisfied with a point at the Veltins Arena.
"Chelsea are a top side with enormous quality. We have a lot of confidence from our recent results as well as our good showings in the Champions League over the past years.
"With the fans in our back, obviously we want to give our best.
"I have always said I want to win every game. But you have to see how the game goes, maybe a draw would be ok and we could live with that situation."
Midfielder Marco Hoger tore his cruciate ligament on Saturday in the 3-2 win against Eintracht Braunschweig, but there was positive news on the injury front.
"We are terribly sorry about the bad injury to Marco Hoger, but Jermaine Jones, Kevin-Prince Boateng and Timo Hildebrand will be back," said the coach.
