• Promise of strong action if Der Spiegel allegations are proved • Potential ban could come into effect as early as next season

Manchester City could be banned from the Champions League, perhaps as early as next season, as Uefa looks set to take strong action should the club be found to have flouted financial fair play (FFP) rules. An independent investigation by European football’s governing body into City’s behaviour was recently opened after information was made public by the Football Leaks hack and published in the German magazine Der Spiegel alleged City used sponsorship deals to circumvent rules on how much money owners can put into a club.

At a meeting of Uefa’s executive committee in Dublin the president, Aleksander Ceferin, described the investigation as “a concrete case” and pledged an outcome “very soon”. Uefa officials believe the integrity of one of the organisation’s key rules is under threat and that sporting sanctions are the only appropriate response should City be found to have flouted them.

Manchester City FFP allegations examined by Uefa officials Read more

The Premier League champions were previously fined £49m for contravening FFP in 2014 but avoided a more severe punishment and subsequently had the fine reduced to £18m after complying with operational and financial measures agreed as part of the punishment.

Emails published as part of the Football Leaks revelations, however, suggest that City’s actions had been deeper and more widespread than initially thought.

In one correspondence Jorge Chumillas, City’s chief financial officer, appears to reveal that an apparent sponsorship deal by Etihad Airlines, worth £68m to the club, was in fact largely to be paid directly to City by the club’s owners, the Abu Dhabi United Group (ADUG).

Der Spiegel also claimed that as City began to become concerned about failing to meet FFP standards they set up a “closed payment loop” in which ADUG paid a third party to pay City for the image rights to their players. Known internally as “Project Longbow”, it allegedly generated revenues of £11m a year for the club. The Guardian has not seen or been able to verify the documents Der Spiegel has used in its reporting.

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City have issued a consistent response to all claims made by Football Leaks and Der Spiegel: “We will not be providing any comment on out-of-context materials purportedly hacked or stolen from City Football Group and Manchester City personnel and associated people. The attempt to damage the club’s reputation is organised and clear.”