Sporting director Christian Heidel has claimed Schalke had no other option but to sell Leroy Sane to Manchester City after the Germany international filed a transfer request.
The 20-year-old left Gelsenkirchen to join the Premier League side for a fee believed to be £37 million, potentially rising to £46m, but Schalke would have preferred to hold on to the promising attacking midfielder for at least one more season.
"It was a very hard decision to sell Sane, but we had no other option," Heidel told Bild.
"Of course, Schalke have lost an amazing player, who knows exactly what he wants and with whom I have had some very pleasant conversations. He wanted to leave, though, and a transfer was in Schalke's best interests as well in the end.
"I obviously regret losing him, but it was my job to make as much money as possible out of him when it became clear that he wanted to leave.
"But that obviously does not mean Schalke will sell anyone who tells me that he wants to leave."