The Bavarians are sixth in the league and all but out of the Champions League after Tuesday's 2-0 home defeat to Girondins Bordeaux, with pressure mounting on coach Louis van Gaal.
"I am sure this will be a tough match but it is possible to beat Bayern," Schalke striker Jefferson Farfan told his club website.
"Great clubs like Bayern who have such good players are always under pressure. We won't think about their problems and we will just focus on playing our game successfully," the Peruvian said.
Schalke are enjoying a successful first season under coach Felix Magath, and despite no major signings this year, they are fourth on 21 points, two points ahead of Bayern.
"There is always a chance to beat Bayern. We will not hide in the back," said Magath, a former Bayern coach himself.
With Schalke strikers Kevin Kuranyi and Farfan in fine form having scored more than half of their team's goals so far and veteran Marcelo Bordon imperious in the back, the wounded Bavarians have their work cut out.
Bayern playmaker Franck Ribery will still be missing through injury although a fully recovered Arjen Robben should start after coming on as a substitute against Bordeaux.
Striker Luca Toni is set to grab a spot ahead of Mario Gomez and Thomas Mueller will return in midfield after his Champions League suspension.
Van Gaal gave his players a rare day off on Thursday to flush the midweek defeat out of their system, knowing that a defeat against Schalke would make his position uncomfortable.
"The day off is for the heads to clear and turn to focus on Schalke," van Gaal told reporters. "This is a crucial match which we must win."
Bayer Leverkusen, top on 23 points, take on Eintracht Frankfurt on Friday as they look to extend their unbeaten run this season.
Werder Bremen, one point behind in second place, host Borussia Dortmund and third-placed Hamburg SV travel to Hanover 96 on Sunday.
