Bayern Munich manager Thomas Tuchel apologised to Harry Kane after the England captain's debut ended in a 3-0 defeat to RB Leipzig in the German Super Cup on Saturday.
Kane was named among the substitutes having sealed his €100 million move to Bayern from Tottenham just hours earlier. He made his first appearance off the bench in the 64th minute with his side already trailing 2-0 thanks to a Dani Olmo double.
Kane was unable to inspire a Bayern fightback as Olmo stole the show, completing his hat-trick minutes after Kane was introduced to seal an impressive win for German Cup holders Leipzig.
"I'm just sorry for Harry Kane, he probably thinks that we haven't trained for four weeks," said Tuchel, who admitted he was at a loss for words for the Bundesliga champions' limp performance.
"It's frightening, unexplainable," he said. "It was the case last season and clearly we have completely disintegrated to that frequency again today."
Kane, England and Tottenham's record goalscorer, had been the star attraction leading up to the match at Bayern's Allianz Arena, with fans lining up hours before kick-off to get their "Kane 9" shirts printed at the club store.
Kane, who was given the No 9 vacated by Robert Lewandowski last summer, had indicated on social media that he was "feeling good" and "looking forward to the match" after taking part in his first training session as a new Bayern player.
But he couldn't turn the tide as Leipzig were awarded a penalty three minutes after his introduction. Olmo converted the spot-kick to seal a first Super Cup title for Marco Rose's side.
Kane, who has lost three finals with Tottenham and one with England, must wait for his first ever trophy.
Leipzig had earlier stunned the Allianz Arena, taking the lead inside three minutes. David Raum's free-kick wasn't dealt with by Bayern and Olmo calmly stroked the ball beyond Sven Ulreich.
Harry Kane's Bayern Munich debut – in pictures
Things went from bad to worse for Bayern when Olmo scored a fabulous second to double Leipzig's advantage a couple of minutes before half-time. The Spaniard's deft pivot around Bayern defender Matthijs de Ligt allowed him the space to slot it calmly beyond Ulreich.
Kane, 30, has moved to Bayern after two decades at Tottenham where he was constantly thwarted in his bid for trophies.
"I felt like it was the time to leave. I didn't want to go into the season with a lot of unresolved future talk," said Kane in a message on social media.
"Obviously a lot of emotions going through me right now; sad to be leaving the club I've spent nearly 20 years of my life at, from 11-year-old boy to a 30-year-old man now.
"There's been so many great moments and special memories, memories that I will cherish forever."
After protracted negotiations between Bayern and Spurs chairman Daniel Levy a deal was finally struck on Thursday.
"It's been a long process, but now we're all the happier that Harry Kane will be wearing the Bayern Munich shirt with immediate effect," said Bayern CEO Jan-Christian Dreesen.
"Harry Kane was our absolute dream player right from the start. He is a perfect fit for us and the club's DNA in terms of both football and character."
Six-time European champions Bayern were in desperate need of a striker after struggling to replace Lewandowski, who left for Barcelona last season.
The club won the Bundesliga in each of Lewandowski's eight seasons in Munich, with the Pole averaging 30 goals per season. In 2022-23, not one Bayern player hit the 15 league goal mark.
Kane had scored more than 20 league goals in all but three of the past nine Premier League seasons, winning the Golden Boot on three occasions.
Kane, who was out of contract next summer, left Tottenham having scored 280 goals in 435 games to become the club's all-time leading goalscorer, but without a trophy.
He is also England's all-time top goalscorer with 58 international goals.
Silverware is all but guaranteed at Bayern, who have won 11 straight Bundesliga titles.
However, Bayern were eliminated by eventual winners Manchester City in the quarter-finals of the Champions League last season and only won the Bundesliga title on goal difference thanks to a final-day capitulation from Borussia Dortmund.