Thomas Tuchel was reportedly warned about his negative behaviour by Bayern Munich's board at a secret meeting during the recent international break.
Tuchel arrived at Bayern less than six months ago when he replaced Julian Nagelsmann, but has already tested the patience of his new bosses, particularly during the summer transfer window.
The German giants managed to sign Harry Kane from Tottenham for £100m, but Tuchel also wanted Declan Rice before he moved to Arsenal, Manchester City's Kyle Walker, and was frustrated that the club missed out on Fulham's Joao Palhinha on deadline day.
Bayern chiefs were unimpressed by Tuchel's 'erratic' conduct following the failed transfers, and called him in for a secret meeting earlier this month while the players were away on international duty, according to Bild.
Tuchel was told to be less negative and emotional when talking about his team in public, while the club are also concerned his comments could be upsetting his players, and gave him a strict warning that he needed to change.
The 50-year-old has endured a difficult start at Bayern, having arrived with a potential Treble on the cards in the latter stages of last season.
Those chances quickly went up in smoke when Bayern were knocked out of the German Cup by Freiburg in Tuchel's second game in charge.
They were then swatted aside by Manchester City in the Champions League quarter-finals, and needed a final day collapse from Borussia Dortmund to retain their Bundesliga title.
Bayern began this season ominously by thrashing Werder Bremen 4-0 but have looked less convincing since then, and were held to a 2-2 draw by Bayer Leverkusen last Friday.
The team return to Champions League action tonight when they host Manchester United at the Allianz Arena.
Tuchel will not be on the touchline for the clash as he serves a one-match suspension.
The German coach was sent to the stands during Bayern's 1-1 second-leg draw with City in April, and was subsequently handed the punishment of watching tonight's game away from the dugout..