Dortmund chief executive Hans-Joachim Watzke has criticised Manchester City's spending following comments made by Pep Guardiola regarding the amounts the Bundesliga club have paid out in agent fees.
City face Dortmund in the second leg of the Champions League quarter-final on Wednesday night, with Guardiola having previously claimed that the Germans "pay a lot of money" to agents to secure top young talent.
Reacting to those comments, Watzke has pointed the finger at City's spending in recent years, which has seen the Premier League leaders assemble a squad considered one of the strongest in Europe.
What did Guardiola say?
In advance of the first leg of the last-eight tie, that City won 2-1 at Eithad Stadium, Guardiola told reporters: "If one person knows in Manchester about Borussia Dortmund it is me. The culture of this club, the way they play and I will not find one single player from Borussia Dortmund without quality.
"They spend a lot of money on young players and pay a lot of money to agents to bring these players there because they have an incredible quality. Incredible. Maybe they didn't find this season the consistency in the Bundesliga to win every week but for two [knockout] games they are able to do anything."
What has Watzke said in response?
"In the last five years they [City] have spent nearly €1bn (£870m/$1.2bn) on new players," the 61-year-old told BBC Sport. "In five years. Who has the possibility to make this? He has not to criticise other clubs.
"[Dortmund's strategy] is working fantastic but it is difficult to develop a team with it because after two or three years, these young players, if they perform very, very well, like Erling Haaland or Jadon Sancho, then the biggest clubs in Europe want to buy them. This is the only way for Borussia Dortmund.
"Dortmund is not a club where you must have big visions because you don't have big money.
"If I had money like other clubs, who can spend €1bn in five or 10 years on the team, then you can have visions. What I want to have for the next years is that we get the status to be one of the best 10 or 12 clubs in Europe and normally to win some titles in Germany."
How much have City spent on players?
Since succeeding Manuel Pellegrini in 2016, Guardiola has spent in excess of £750m ($1bn) on new players, starting with Ilkay Gundogan, who arrived for around £20m ($28m).
The City boss also signed Leroy Sane, Gabriel Jesus and John Stones, for initial fees totalling around £111m ($152m), in his first transfer window in charge, while Bernardo Silva, Benjamin Mendy, Kyle Walker and Ederson all arrived in 2017 for big fees.
Guardiola then moved to bring in Aymeric Laporte from Athletic Club for a then club-record £57m ($78m), before that fee was topped by the signing of Riyad Mahrez from Leicester City for £60m ($83m).
There were further reinforcements in 2019, with Joao Cancelo and Rodri joining from Juventus and Atletico Madrid respectively, and in 2020, City moved for Ruben Dias in a transfer worth around £65m ($89m).
Nathan Ake, who has featured sparingly in the 2020-21 campaign, also arrived from Bournemouth for £40m ($55m) - a club-record sale for the Cherries.
City have been linked with moves for Erling Haaland and Harry Kane when the summer transfer window opens, although Guardiola has insisted his side cannot afford to pay the "impossible" prices that have been reported in the media.