Referee Wolfgang Stark has admitted he made a mistake not showing Paderborn's Marvin Bakalorz a red card for his foul which may well leave Marco Reus sidelined for many months.
Bakalorz, who played for Dortmund for three years, made the reckless challenge during the two side's 2-2 draw on Saturday with Reus carried away from the field with suspected ankle ligament damage.
Having seen the incident again, FIFA referee Stark has admitted it should have been red and not the yellow card that he showed.
"The way I saw it during the game, Bakalorz slid in to get the ball and he made the slightest of contacts with it before then hitting Reus,'' Stark told the Bild newspaper.
"For me, it was a foul and a yellow card. When I saw the replay afterwards, I was shocked and I've got to say that red would have been the right decision.''
Aside from his own decision, Stark regrets the latest injury which is likely to leave Reus on the sidelines for the third time this season.
"We had a chat during the warm up and I told him how glad I was to see him back and fit again,'' Stark said. "I really hope the injury turns out not to be so bad.''
That feeling is shared by Dortmund coach Jurgen Klopp. "It's an incredible scene and there are no other words to describe it,'' Klopp said.
"Marvin's a great lad, but that was just too much. He'd been sliding in all game and I'd told him that he shouldn't be doing it.''
Bakalorz added: "Klopp screamed at me, and he's absolutely right to too.''
His coach Andre Breitenreiter has also defended him, saying: "Anybody who knows Marvin Bakalorz knows how much he loves Borussia Dortmund.
"Marvin was as white as a sheet. We're all terribly sorry, even if we can't change it now.''