Bayern Munich manager Thomas Tuchel said his team "played today like it didn't matter", calling the shock 1-0 home loss to Werder Bremen a "huge setback" in the title race.
Bayern's loss on Sunday, their first against Werder Bremen in 16 years, leaves Xabi Alonso's Bayer Leverkusen seven points clear atop the Bundesliga table.
Tuchel's men have a game in hand, to be played at home against struggling Union Berlin on Wednesday.
Bayern spent the majority of last week at a warm-weather training camp in Portugal.
"You have to ask the players," Bayern manager Thomas Tuchel told DAZN when asked why the performance did not match up to what the team produced on the training pitch.
"We played today like it didn't matter, as if we were 10 points ahead and had a Champions League match to play on Tuesday.
"After the Leverkusen result, we wanted to start aggressively and send a signal, but we didn't succeed at all."
Pre-match, Tuchel praised his side's performance at the Portugal training camp, but said afterwards "I don't have any desire to keep saying that we trained well, because nobody will believe me when we play like that."
Speaking at the post-match press conference, Tuchel called the result "a huge setback" as they hope to keep pace with Leverkusen, who have dropped just six of a possible 54 points so far this season.
Leverkusen came from behind twice to beat fourth-placed Leipzig 3-2 on Saturday, the second-straight week where they scored an injury-time winner.
"For 70 minutes we didn't play like a team who wanted to win a championship" saying his side "deserved to lose."
Bayern were held scoreless in the league for the first time in almost four years dating back to February 2020, with striker Harry Kane failing to add to his goal tally of 22 from 17 games this season.
"If we play like that we will have big problems on Wednesday (against Union)" Tuchel said.
"We have to take action, to find solutions. I have to find solutions."
Bayern veteran Thomas Mueller told DAZN it took his team "70 minutes to realise" they had to break out of the "sluggish and lifeless" performance.
Eliminated from the German Cup by third-division Saarbruecken, Bayern face Italian side Lazio in the last 16 of the Champions League.