Hannover admit they're angry over leaks confirming their pursuit of Getafe winger Pedro Leon.
The German club made the approach this summer, offering one million euros (£795,000) plus a sell-on arrangement, according to the document.
The Bundesliga club are unhappy the approach for Leon has been made public.
"I've never experienced anything like it," Hannover director of sport Dirk Dufner told Bild newspaper.
"We're the victims here and we have been abused. There are no rules for this kind of thing in football.
"Pedro was one of five or six options for the right-hand side of our midfield."
