Coach Pep Guardiola has demanded an immediate reaction from his Bayern Munich side in Wednesday's German Cup semi-final in the wake of the Bundesliga champions' worrying league slump.

"I need to find a way to help us recover our rhythm ready for the challenges that lie ahead," said Guardiola, whose side host second-division Kaiserslautern in Wednesday's semi-final for a place in the May 17 final.

"My goal as coach is to help the team pick themselves up. We need an immediate reaction."

The Bundesliga champions suffered their heaviest home league defeat since 2008 on Saturday when their full-strength side was trounced 3-0 at home by second-placed Borussia Dortmund, who rested star striker Robert Lewandowski for the first hour.

Bayern face Real Madrid in the Champions League's semi-finals later this month and are bidding to repeat last year's treble of European, league and cup titles.

But the Bavarian giants are winless in their last three league games, including back-to-back defeats, since wrapping up the Bundesliga title with a record seven games to spare.

"We need to learn our lessons and talk a few things over. We get back to work on Monday with our focus on the future," said director of sport Matthias Sammer.

"We want to see the real Bayern Munich again. We need much better performances than against Dortmund."

Just three days after beating Manchester United 3-1 in Munich to reach the last four of the Champions League, Bayern were humbled at home as Henrikh Mkhitaryan, Marco Reus and Jonas Hofmann netted Dortmund's goals in the top-of-the-table clash.

"We were obviously hoping for a totally different performance in front of our own fans," said Bayern's Germany forward Thomas Mueller.

"A few things failed to gel and as a team, we weren't as fresh and hungry as we should be and want to be.

"There have been times this season when we've been in much better shape."

In the build-up, Bayern had insisted it was a meaningless match with the title decided and just bragging rights at stake, but the heavy defeat against Guardiola's first-choice side gave cause for concern.

"We were unable to maintain our concentration at 100 percent from the start against top-class opponents," said Sammer.

"We weren't focused enough in the decisive phases of the game.

"We rather handed it to Dortmund on a plate.

"The players aren't robots or machines. We're champions and the league is done and dusted, so it's not the end of the world."

To compound Bayern's problems, wing-back Rafinha was sent off late in the game for striking Mkhitaryan in the face.

Germany goalkeeper Manuel Neuer missed the second-half with a minor calf problem, but expects to play on Wednesday.

"We simply had a bad day at the office," said Neuer.

"I think we have different and more important challenges, but we can't just give up on the Bundesliga."

With four games left before Bayern are presented with the Bundesliga trophy on May 10 at home to VfB Stuttgart, Munich are at bottom side Eintracht Braunschweig on Saturday.