Borussia Dortmund sporting director Michael Zorc told ESPN FC his team's efforts in Saturday's 2-2 draw against Freiburg had been "simply not enough in every aspect."
Dortmund continued to struggle under newly-appointed coach Peter Stoger and are winless in 2018 after three matches.
Only Jeremy Toljan's last-gasp equaliser saved them from a home defeat, and Zorc was scathing after the game.
"Nothing indicated today's performance," he said. "The week in training went very well.
"We scored to go 1-0, played formidably and, all of the sudden, we started to do less and less. I cannot explain this performance.
"We lacked courage -- it was simply not enough in every aspect. I have to admit that I'm rather speechless."
Shinji Kagawa opened the scoring after nine minutes but Nils Petersen levelled and then struck again to put Freiburg on the brink of victory until Toljan's late effort.
And a frustrated Zorc added: "Freiburg were beatable. If we play well, we come out as winners today."
Dortmund are in danger of losing further ground on the top four places that guarantee direct qualification for the Champions League group stages, and Zorc said: "Of course I'm worried, especially as we had two home games, in which we thought we would pick up much-needed points."
Goalkeeper Roman Burki criticised fans who booed the team in an interview with Sky after the game, saying it did not help and suggesting those fans ought to stay at home.
Zorc said: "I'm not sure what induced him to make such a statement. I find that statement unfitting and factually incorrect.
"I would advise the players that were on the pitch today to re-watch the game in its entirety. Then they have to watch out that they won't start booing themselves.
"I don't think the reactions were too harsh. It's the fans' right to air their discontent if the game is going badly."
Zorc refused to blame the uncertainty surrounding Pierre-Emerick Aubameyang's potential transfer to Arsenal for Dortmund's difficulties.
"We failed to win the third game in a row," he said. "Two times he wasn't part of that, today he was. I don't think that this was the deciding factor.
"I wouldn't make too many distinctions between performances [of the players] today. Just look at our passing in midfield and how many tackles we didn't win. Overall, it was simply weak.
"This performance is not what we expect of every single player in a black and yellow shirt. Every player has to look carefully at how he can improve now."
Coach Stoger admitted Aubameyang had not been at his best, telling a news conference: "I would say he has had better games. On the one hand, it certainly wasn't his best game but, on the other, we didn't manage to give him decent service.
"In the end, he is part of a larger group of players who didn't have their best performance."