"Bayern Munich want to destroy us," said Borussia Dortmund chief executive Hans-Joachim Watzke after Robert Lewandowski became the latest of his players to agree a switch to the Allianz Arena in January.
The Poland striker scored his first goal against his former club in Bayern's 2-1 win on Saturday to help condemn Dortmund to a fifth straight league loss and leave them third from bottom in the Bundesliga.
So, with Marco Reus possibly following Lewandowski and Mario Gotze to Munich, are Bayern to blame for the 2013 Champions League finalists' decline?
Jurgen Klopp's Dortmund revolution
A Champions League final, two Bundesliga titles and a German Cup: Jurgen Klopp has helped Die Schwarzgelben return to the European elite from the brink of bankruptcy since being appointed coach in July 2008.
Dortmund were no stranger to success, having won the Champions League in 1997, and winning three Bundesliga titles between 1995 and 2002, but when Klopp arrived from Mainz the club was on the brink of collapse.
Dortmund chief executive Hans-Joachim Watzke told FAZ in 2013 that the club was "a millimetre away from going bust" during that period. Between 2004 to 2008, they finished sixth, seventh, ninth and 13th.
Their re-emergence began when Klopp was appointed as they won the Bundesliga in 2010-11 with the youngest team ever to win the domestic title. The following year, Dortmund successfully defended their title and won the German Cup, to make it a historic double.
"Klopp has done a brilliant job," said NDR Radio reporter Alexander Bleick. "When he took over, Dortmund were a middle class team."
From champs to chumps
Bayern emphasised their Bundesliga dominance last season when they defended their title with a record seven games to go, finishing 19 points above runners-up Dortmund.
Few would have predicted what was to follow though, with Saturday's defeat by Bayern leaving Dortmund 17 points behind their rivals after just 10 matches and, with just seven points, sitting in the bottom three.
Their worst ever start to a Bundesliga campaign is contradictory to their Champions League form, where Dortmund sit top of Group D with three wins out of three and yet to concede a goal.
Striker Pierre-Emerick Aubameyang told BBC World: "It is true you almost get the feeling we have two faces at the moment. One in the Bundesliga and one in the Champions League."
When did it all go wrong?
The 2013 Champions League final defeat to Bayern is seen by many as the moment things started to go wrong.
Had Dortmund been crowned kings of Europe, perhaps they would have been able to prevent their stars from deserting to the Allianz Arena?
This seems a little simplistic as the signs of Dortmund's collapse were already in evidence. Star midfielder Mario Gotze's £31.5m move to Bayern was announced on the eve of the Champions League defeat for starters.
Also that season, Dortmund may have been Bundesliga runners-up but they finished 26 points behind champions Bayern to suggest the latter's dominance had already begun.
The key departure this summer was Robert Lewandowski's move to Bayern after 101 goals in 185 appearances for Dortmund.
Klopp was busy in the transfer market over the summer in a bid to replace him, signing last season's Serie A top scorer Ciro Immobile from Torino, sealing the return of Shinji Kagawa from Manchester United and buying Adrian Ramos from Hertha Berlin.
But they have just 10 goals after as many matches this season, compared with 22 goals at the same stage last season.
"They haven't been able to replace Lewandowski," said Bleick. "They have tried but they lack the self-confidence to score the goals. "
'Copycat' Bayern Munich to blame?
So it is all Bayern's fault then? Maybe not, but it is fair to say relations between the two clubs are not good.
The traditional pre-match lunch between Bayern and Dortmund bosses was scrapped yesterday after a war of words between the two clubs that has been ongoing almost ever since Gotze's £31.5m switch.
Their relationship hasn't been helped by Bayern's recent pursuit of Marco Reus, Dortmund's 25-year-old Germany midfielder.
Watzke told Bild in January: "They have helped themselves to our players, so we wouldn't be a danger."
|Bayern splash the cash|
|In the past four seasons, Bayern Munich have spent in the region of £56.5m compared to Dortmund's estimated £36.5m|
|In that period Bayern have received around £16m for sales, while Dortmund have received an approximate £52m|
He also told TZ last month: "There are players here at Dortmund who are happy to play for 20% less money. But that's not the case when we're talking about 50% less money. It's like they (Bayern) want all of our players."
Bayern chief executive Karl-Heinz Rummenigge responded in Saturday's match programme: "We don't have to weaken anybody. Every transfer has exclusively one goal, to strengthen the team's quality."
"A few years ago the two clubs had quite a good relationship," said Bleick. "But when Borussia Dortmund won the title twice, they were celebrating quite offensively, saying 'we are back now'. Bayern did not like that.
"When Dortmund beat Bayern 5-2 in the German Cup final, the celebrations were extraordinary. Bayern decided they have to get back and spent a lot of money and the relationship got worse.
"Dortmund believe Bayern Munich want to destroy their work."
Other reasons for downfall
To blame Bayern's transfer policy for Dortmund's decline would be too easy.
Sporting director Michael Zorc said: "We've made unbelievable mistakes in the defence, like never before."
"Bayern Munich's signing of Dortmund's players is just one factor," said Bleick. "Although the main problem is replacing Lewandowski.
"Injuries have not helped either and when they get their players back I think we will be looking at Dortmund improving."
Striker Aubameyang believes motivation has been a factor in Dortmund's struggles this season, admitting the Champions League games feel different.
"I think we are going to have find extra motivation in the league," he told BBC World. "When you are playing in the Champions League there is no need to have extra motivation because the games are so special."
Always look on the bright side
"Despite Dortmund's struggles there are no whistles or posters against the manager from the supporters," said Bleick. "They still admire and support him."
One woman even made a declaration of love during a news conference before the match against Bayern on Tuesday, saying to Klopp: "You led us to success and we will lead you through the crisis."
During BBC World's visit to Dortmund at the weekend, statements from the fans included "nothing much is wrong", "They are not so hungry", "I think they will come again".
Bleick continued: "Dortmund aren't so strong as they were last year but in a couple of months, I think we will be talking about them back into eighth or ninth.
"Bayern Munich are becoming quite untouchable, other teams don't have the depth to catch them. If they struggle in the Champions League again this season I expect them to spend a lot of money again."
Klopp said of Bayern's pursuit of Reus last week: "I believe life is fair and if you misbehave while you are successful, you will get it back one day."
He may have to wait a while to get his revenge but there is no shortage of belief he is still the man to achieve it.