The translator had just reached the final line of Jürgen Klopp's pre-match conference and was thanking everyone for coming, when the Borussia Dortmund coach intervened for one last time. "I've got something to say," he announced, glancing up at the line of cameras at the back of the room as if addressing his audience directly, looking them in the eye. Then came the plea: "I would like to ask the fans to give us the support we need tomorrow night."

It was the third or fourth time that he had delivered much the same line. That he felt the need to finish on that note, to repeat himself again, illustrated how much the news had hurt, how this historic moment had been hijacked by the disclosure that Bayern Munich had secured a €37m (£31.5m) deal to sign Mario Götze from Dortmund at the end of this season by triggering a buy-out clause in the midfielder's contract.

Bayern, who loom over the rest of the country and threaten the remainder of the continent too, have reached two European Cup finals in the past three years and have already clinched the league, with the domestic cup final to come. They have a budget twice the size of any side in Germany and debilitating their rivals is not a new tactic. This signing follows the €40m signing – again via a release clause – of Javi Martínez from Athletic Bilbao last summer. Barcelona had also shown an interest but found themselves unable to compete. And of course, the new manager will be Pep Guardiola. Götze was his personal target.

The focus here was more immediate. For Dortmund the risk of a derailment on the eve of this semi-final against Real Madrid is evident. "I don't know Mario Götze, I don't know the mentality or culture of the fans of Dortmund and I don't know what the players will be thinking," José Mourinho, the Madrid coach, said, "so I don't know if it will have positive or negative consequences, or no consequences at all." The latter appears unlikely in the extreme. Klopp was determined that the focus on Wednesday night should be on his side and Madrid, not Bayern or their new signing. Götze is still a Dortmund player.

Klopp found out the story was about to break at 10pm on Monday, though the rest of Germany had to wait until Tuesday morning when Bild's cover shouted: "Götze Zu Den Bayern [Götze to Bayern]." Faced with a fait accompli, the club had little choice but to confirm that it was true – not exactly ideal preparation for Dortmund's first Champions League semi-final since 1998. The timing is so bad as to be suspicious; Klopp first knew about the signing the day after defeating Málaga – "I had one day's happiness," he said – but it was kept secret. Now it has been released. Now.

"It could have been worse: it could have happened a couple of hours before the game," Klopp said. "But on a scale of one to 10, this is a nine. We all know why it has come out now. We don't know why the people who have leaked this have done so at such a delicate time. We can only speculate but we are all making the same suppositions."

Most took the hint. Bayern Munich's president, Uli Hoeness, has reported himself to police for tax evasion. Conveniently that is now yesterday's news. Yet asked directly if he thought that Bayern had leaked the news and timed it with malicious intent, he replied: "I don't think Bayern, Götze or his representatives have any interest in harming us today."

At one stage Klopp joked with Martin Ainstein, an Argentinian journalist with the deep, earthy voice of a Hollywood announcer. Responding to a question that began "I would like to know", Klopp said: "What I would like is your voice." There were other jokes, too, and he was measured in his responses, saying that fundamentally neither Bayern nor Götze had done anything wrong, but there was no escaping the hurt, the damage. The coach admitted he had not yet had the chance to speak to his players.

"This is a special situation. We chose to hold the press conference before the training session so we have not been able to design a plan of action. I have spoken to some of them by phone but I will have to speak to the others during the session," he said. "We are incredibly disappointed but we cannot ignore the fact that this was done according to his contract. We don't like [Bayern paying Götze's buy-out clause] but we did the same this season with Marco Reus and Borussia Mönchengladbach weren't happy either."

He continued: "Götze has gone because he is Guardiola's personal chosen signing and he wants to play with Guardiola, in his style. I can't make myself 15cm shorter or start speaking Spanish. I cannot preach a football based on quick transitions and then [suddenly] start playing tiki-taka.

"We're hurt but this makes us even more determined," Klopp continued. "If there are any fans who cannot leave their disappointment behind them, I would ask them not to come and instead to give their ticket to someone else. I don't know why they would release this now but if they want to make it so that we do not win, I can tell them that they will not succeed."