Borussia Dortmund CEO Hans-Joachim Watzke says his club must take a stance against Ousmane Dembele's behaviour to set an example for the rest of the Bundesliga.
Dembele is currently serving an indefinite suspension at Dortmund after skipping training last week in an attempt to force a move to Barcelona. The 20-year-old has has returned to his native France.
Watzke addressed the issue after Dortmund's 3-0 rout of Wolfsburg on Saturday, telling reporters: "We should not talk about how this looks for a club that is registered as stock company."
And he said Demebele's action should serve as a warning to other German clubs.
"The whole Bundesliga should maybe see how important it is that we are showing strength now," he said. "[Dembele's behaviour] is not only a topic on our door but could affect all 17 other clubs eventually.
"So they can be happy that we are ramming down a big, fat stop sign."
Sporting director Michael Zorc had revealed earlier on Saturday that Dortmund will not wait until the last day of the transfer window to sell Dembele.
But Watzke was coy on naming a deadline for Barcelona, saying: "We will give notice to our Catalan friends in some form."
Asked if Dortmund and Barcelona are in constant contact, Watzke said: "No, they know what we want to have. So we don't have to be in regular exchange.
"They should tell us whether they want to [make the transfer] or should leave it. Then [Dembele] is back with us at Sept. 1 -- there are only those two possibilities."
The clubs might not be talking often, but Dortmund striker Pierre-Emerick Aubameyang said he is staying in touch with Dembele.
"Yes, all the time. I am in contact with him," he said. "It is a difficult situation for him and for the club. That's all I can say. I understand the club, I can also understand him."
Asked what they talked about, Aubameyang said: "Nothing special. It's his future, so he has to make the decision."
Watzke was happy with his team's dominant performance at the Volkswagen Arena, finding praise for newly appointed coach Peter Bosz.
He said: "I read everywhere that we would have problems in adjusting [to the new coach]. I didn't see any problems there. The team did well to follow the coach's instructions.
"We were very aggressive on attacking the ball, and still, I thought we had a good mix in winning the ball aggressively and calming the match down.
"That was a very mature performance. But we also don't have to overstate this, as it did not come as a surprise to us, because even if there are outside factors like Neymar [transferring to PSG] that we cannot influence we always had serenity within the club.
"Again, we mustn't overstate the win, but it was a very content performance."