But Der Spiegel has now published details

from its own investigation conducted in conjunction with the European Investigative Collaborations (EIC) journalism network.

It offers detail on each of the three areas it claims form the focus of the Premier League's enquiries.

The Premier League and Manchester City declined to comment when approached by BBC Sport.

However, it is understood City believe the latest details are a continuation of previous allegations in relation to Financial Fair Play regulations, which they feel are designed to damage the club. It is thought the club also want to respect the ongoing process with the Premier League by not commenting.

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.

Analysis

BBC sports editor Dan Roan

These revelations threaten to reawaken the controversy that has long surrounded the finances of the dominant force in the English game, despite City's previous denials of wrongdoing.

While City successfully appealed against a Champions League ban in 2020 after Cas handed the club a landmark victory over Uefa, they were still heavily criticised for a "severe breach" of regulations by failing to co-operate with Uefa's investigative process.

Meanwhile, a Premier League probe - originally launched in 2018 - continued. And now we have been told what it allegedly involves.

Last year a court of appeal judge expressed his concern at how long the inquiry was taking, saying that it was "a matter of legitimate public concern, that so little progress has been made…"

According to Der Spiegel, that investigation drags on, and league bosses could now come under pressure from other clubs to reach a conclusion. It has been suggested that the league does not have the same time limitations on its investigative power as Uefa did.

By the time its investigation is completed, however, City could easily have claimed a fourth title in five years.