Dutchman Bosz initially lived up to his reputation when Dortmund raced to six wins in their first seven league matches.
A quick passing game with even quicker counter-attacks sent Dortmund above champions Bayern Munich in the table.
But as soon as Bosz's team started to stutter, results suffered.
From first place only a few weeks ago, Dortmund have dropped to fifth, having lost four of their last five Bundesliga matches -- along with their confidence -- and their last victory was back in September.
Dortmund top scorer Pierre-Emerick Aubameyang has not netted in the Bundesliga since mid-October while the once solid backline is the very picture of inconsistency, with errors commonplace between defenders and keeper Roman Buerki.
Two of those gave Tottenham Hotspur the chance to come from a goal down to beat them 2-1 on Tuesday and eliminate the Germans from the Champions League.
Finalists in 2013, Dortmund must now battle for a spot in the second-tier Europa League, but before that they have to face Schalke in the most fierce of the country's football rivalries.
"When you are at a big club like Dortmund then you have to win, and when you don't for a longer period of time, then pressure mounts," Bosz, whose team have not won any of their five European matches so far, said after Tuesday's loss.
"That's why this derby is very important. I think that the derby comes at just the right time for us in our current situation," he said. "All the players, especially those who have been here longer, know how important this derby is."
But he knows he has only a few days to pick his players up and lead them back to winning ways.
"We are lacking self-confidence at the moment and when you fail to win for such a long time then it is only normal," Bosz said.
Schalke, with four wins in five matches, are currently firing on all cylinders, having climbed into second place on 23 points, three ahead of Dortmund, with Bayern top on 29.
Bayern travel to fourth-placed Borussia Moenchengladbach while RB Leipzig, in third, also on 23, host Werder Bremen.
(Reporting by Karolos Grohmann,; Editing by Neville Dalton)
