Covid-hit Bayern Munich crashed to a 2-1 defeat at home to Borussia Moenchengladbach Friday with the Bundesliga leaders forced to name a makeshift team after nine stars tested positive for the coronavirus.
Robert Lewandowski cracked in his 20th league goal this season to give Bayern an early lead, but Gladbach hit back with two goals in four first-half minutes by Florian Neuhaus and Stefan Lainer.
"Gladbach aren't our favourite opponents," said striker Thomas Mueller as Bayern had already crashed to a 5-0 defeat at Gladbach in the German Cup last October.
"It is bitter to lose, but we have to swallow the defeat."
Mueller refused to blame the lose on their depleted squad.
"We had a lot of quality on the pitch and we shouldn't have given away so much possession in the final third of the pitch," he said.
"The worst thing is we didn't put our chances away," Mueller admitted after he twice came close to grabbing a second-half equaliser.
Despite the defeat behind closed doors in Munich, Bayern remain nine points clear at the top of the table, but second-placed Borussia Dortmund can trim the gap on Saturday at Eintracht Frankfurt.
Gladbach climbed three places in the table to 11th, but still remain only five points from the bottom three places.
With so many of his stars sidelined by Covid, Bayern coach Julian Nagelsmann named a patched-up squad with six reserve team players on the bench while forward Malik Tillman, 19, started his first Bundesliga match.
He was replaced in the second-half by Paul Wanner, who at 16 years, 15 days became the youngest Bayern player to make his German league debut having been called up from the club's Under-19 team.
Germany star Joshua Kimmich, who missed the previous two months with Covid, played at right-back with another defensive midfielder Marcel Sabitzer named on the left of defence.
Gladbach were also missing US defender Joe Scally and Swiss midfielder Denis Zakaria, who both also tested positive for Covid.
Bayern took a deserved lead in wintry conditions when Lewandowski hammered an unstoppable shot inside the post past goalkeeper Yann Sommer with 18 minutes gone.
Gladbach equalised when the visitors unpicked the Bayern defence and moved the ball to Neuhaus, who fired past Bayern stand-in goalkeeper Sven Ulreich.
First-choice keeper Manuel Neuer is quarantining in the Maldives after testing positive for Covid-19 on holiday.
Ulreich was again beaten from a corner soon after when Lainer flicked in a header with half an hour played.
Neuhaus and Swiss striker Breel Embolo missed chances to extend Gladbach's lead while at the other end Lewandowski clipped the post with a stunning shot across the goal.
Bayern dominated long spells of the second-half with Jamal Musiala, Mueller and Kimmich all going agonisingly close while Lewandowski again hit the woodwork, but Gladbach held on.