The Premier League has been investigating the club for three years, the publication says.
Der Spiegel, on the other hand, has recently released the results of its own investigation, which was carried out in collaboration with the European Investigative Collaborations (EIC) media network.
It goes into great depth about each of the three areas it claims the Premier League is looking at. When contacted by BBC Sport, the Premier League and Manchester City declined to comment.
However, it is thought that City believes the new information is a continuation of past complaints about Financial Fair Play standards, which they believe are intended to harm the club. The club is also understood to wish to remain silent in order to respect the Premier League's ongoing procedure.
According to Der Spiegel, the Premier League champions allegedly pressured underage players "to sign contracts with Manchester City through monetary payments, in violation of the rules".
Club sponsors in Abu Dhabi are alleged to have "provided only a portion of their payments to the club themselves", with the remainder reportedly made up by club owner Sheikh Mansour bin Zayed Al Nahyan, a member of the Abu Dhabi ruling family.
City are also accused of paying a "significant portion" of former manager Roberto Mancini's compensation "by way of a fictitious consultancy contract".
In 2020, City had a two-year ban from European club competitions overturned by the Court of Arbitration for Sport after Uefa had ruled they had committed "serious breaches" of Financial Fair Play (FFP) regulations between 2012 and 2016.
The Court of Arbitration for Sport said City had showed a "blatant disregard" to Uefa's investigation into potential FFP breaches, even though it found "no conclusive evidence that they disguised funding from their owner as sponsorship".
Uefa began its investigation into City after Der Spiegel published leaked documents in November 2018 alleging the club had inflated the value of a sponsorship deal, misleading European football's governing body.
During testimony to the Court of Arbitration for Sport, a legal representative of the Finance Ministry in Abu Dhabi claimed Abu Dhabi United Group Investment & Development (ADUG) - which owned Manchester City until last year - was "completely unconnected" to the government of the United Arab Emirates or the Emirate of Abu Dhabi.
In 2021, City lost a ruling by the court of appeal, which confirmed that the Premier League was continuing to investigate the champions for alleged breaches of financial fair play.
City's legal team did not want it reported that it was challenging the jurisdiction of Premier League arbitrators to investigate the case.
