Peter Bosz has revealed how a conversation with Louis van Gaal left him with an important coaching lesson after his difficult spell at Borussia Dortmund.

Bosz was appointed Dortmund coach in the summer of 2017 and enjoyed a promising start despite losing the German Super Cup to Bayern Munich on penalties. However, his fortunes changed dramatically by the middle of October, with a poor run eventually leading to his dismissal before Christmas.

Speaking on Omroep Brabant's Masterclass: The Secret of Peter Bosz, the current PSV coach reflected on the problems he encountered at Dortmund and recalled a revealing conversation with Van Gaal.

Bosz explained that he was told shortly after arriving in Dortmund that Pierre-Emerick Aubameyang was expected to leave for China.

“When I arrived at Dortmund, the technical director said: This is your squad, but there’s still one player leaving: Pierre-Emerick Aubameyang. He’s going to China. We get 87 million euros for him and he will earn 24 million euros net per year there and sign a contract for four seasons,” Bosz recalled, as quoted by PSV Inside.

The coach understood why Aubameyang would be difficult to retain if such an offer materialised. However, the proposed transfer collapsed, leaving the striker frustrated.

“I understood that he couldn’t be kept. That deal only fell through and Aubameyang was angry about it, especially because the sporting director afterwards said in the dressing room: No one is leaving anymore. A week later, Ousmane Dembélé was sold to FC Barcelona for 140 million euros.”

Aubameyang subsequently began arriving late to training and made his frustration clear.

“Aubameyang was furious and showed up one minute late in the dressing room every day. What do you do then as a coach? Then you sit down with him.”

According to Bosz, Aubameyang explained that his frustration was directed at the club rather than the coach.

“He said: It’s nothing against you, coach. It’s against the club. They had promised me I could go, but it didn’t happen. Dembélé was allowed to leave, though. The next day he was late again.”

The situation eventually escalated when Aubameyang allowed a French film crew into the stadium while preparing for the match.

“At one point I had a press conference in the stadium, and then Aubameyang let a French film crew in. He was busy with that a day before the match. That was the last straw. I didn’t select him that weekend,” Bosz said.

The PSV coach later discussed the situation with Van Gaal, who wanted to know what happened next.

“He asked: ‘And then?’ I said: ‘Then I didn't take him to VfB Stuttgart.’ Van Gaal asked again: ‘And then?’ I said: ‘Then we played there on Saturday and on Sunday I had a conversation with the whole squad.’”

Van Gaal continued questioning Bosz.

“Van Gaal: ‘And then?’ I said: ‘Then on Monday he trained with us again.’”

The response from the former Netherlands coach was immediate.

“‘Wrong!’ Van Gaal then yelled.”

Bosz admitted he was shocked by the reaction. Van Gaal believed the Dortmund coach should have taken a much firmer stance.

“Van Gaal thought I should send him away. I said: ‘This guy went to Arsenal in the winter for sixty million euros, so how could I send him away?’”

Van Gaal's final response proved painfully accurate.

“Then he said: ‘No, and then you were the one who got sent away.’ Yes, that was also the case,” Bosz recalled.

Bosz's Dortmund tenure ultimately ended in December 2017. The Aubameyang episode became one of the defining moments of a difficult period, while Van Gaal's blunt assessment offered the PSV coach a lesson in the consequences of managing a major dressing room.