Bayern Munich sporting director Christian Nerlinger blasted his team's 2-1 home defeat against Mainz on Saturday as "pathetic" and said it had "set the alarm bells ringing".
"It was a pathetic performance," said Nerlinger after Bayern's second defeat of the season left them 10 points behind leaders Mainz, who have won all of their six matches.
Bayern, who were Bundesliga and German Cup winners last season before reaching the UEFA Champions League final, are eighth in the table and have now suffered their worst start to a season since 1977-78.
"Mainz were extraordinary today and played very well, but our situation is precarious," added Nerlinger.
"The alarm bells are ringing and we need to see how the team reacts."
Coach Louis van Gaal added: "A lot of our players performed well below their usual level. I believe Mainz can go far this season and why not think about the title?"
Saturday's defeat was Bayern's first against Mainz in eight meetings.
Their problems have been compounded by the absence of influential players Franck Ribery and Arjen Robben through injury.
They have also only scored five goals in six matches and conceded six.