City released a statement following the initial allegations that were made on Friday. The operation, allegedly called Project Longbow by club insiders, allowed them to save €30m (£26.1m) in marketing income, according to Der Spiegel.
The official response from City to Der Spiegel's request for comment remains, "The attempt to damage the Club's reputation is organised and clear".
City CEO Ferran Soriano complained in one memo that ECA members were pushing for the UEFA rules - which many thought could curb the rise of Man City and Qatari-owned Paris Saint-Germain.
Guardiola was also lured to Manchester by City's resources after great success with Barcelona and Bayern Munich.
City executive Simon Pearce is said to have joked in one email that he had become the "de facto MD (managing director) of ADUG", leading Der Spiegel to label the situation a "farce" and slam City: "A club director was controlling the expenditures of the club owner's holding company, money that would travel around the world before landing in the team's coffers".
Instead, the revelation is that City saw FFP, and its support from Europe's elite clubs, as something they needed to "fight". And we want to do what we have to do in terms of the rules.
Der Spiegel is planning to publish further stories related to City on Wednesday and Thursday.
Der Spiegel, crediting Football Leaks, has also alleged the third-party company to which they sold player image rights was also funded by the Sheikh.
City representatives have said the Abu Dhabi-based companies are independent sponsors.
When UEFA were investigating City over FFP, Fordham apparently never came up.
"We will need to fight this", Soriano wrote, according to the magazine, "and do it in a way that is not visible, or we will be pointed out as the global enemies of football". "And of course we want to follow the rules, whether UEFA, FIFA or the Premier League", said the Spaniard, who joined City in 2016.
Der Spiegel said this helped turn nearly 30 million euros ($34 million) into revenue instead of a cost, for the objective of UEFA's investigation of club accounts. But the magazine said the analyst "was having trouble" figuring out "how the [external company] expected to make a return".
Leaked documents have claimed City had secret talks with former UEFA boss Gianni Infantino to help them out with Financial Fair Play, that Sheikh Mansour has been funding Abu Dhabi sponsors himself to pour money into City, and that City (and other English giants) have been involved in discussions to form a European Super League.
Since 2008, City have won three Premier Leagues, an FA Cup and three League Cups, and have spent more than £1.4bn on players.