Hoffenheim have officially apologised to Borussia Dortmund for a high-frequency loudspeaker used to drown out singing by Dortmund's fans last weekend.
Dortmund chairman Hans-Joachim Watzke says his club now considers the case closed.
Hoffenheim say one employee was responsible for producing the noise intended to counteract abusive chants by Dortmund fans directed at the team's main financial backer, Dietmar Hopp. Hoffenheim says Hopp and other club officials were unaware of the employee's move.
Ralf Rangnick, the Schalke coach, insists his decision to leave striker Raul behind in Gelsenkirchen had no impact on his side's dismal 2-0 defeat to HJK Helsinki in the Europa League on Thursday.
Rangnick said fielding Raul in Finland would not have made a difference, adding: "We played into the Finns' hands," he said.
