The Court of Arbitration for Sport (CAS) has lifted a two-season ban imposed on Manchester City by UEFA on Monday.
An initial fine of 30 million euros ($34 million, £27 million) was also reduced to 10 million euros on appeal.
The case against City was reopened when German magazine Der Spiegel published a series of leaked emails in 2018.
But CAS found that “most of the alleged breaches reported by the Adjudicatory Chamber of the CFCB (UEFA Club Financial Control Body) were either not established or time-barred”.
Manchester City welcomed the decision that will have huge ramifications on the club’s finances and potentially the future of manager Pep Guardiola and star players such as Kevin De Bruyne and Raheem Sterling.
“Whilst Manchester City and its legal advisors are yet to review the full ruling by the Court of Arbitration for Sport (CAS), the club welcomes the implications of today’s ruling as a validation of the club’s position and the body of evidence that it was able to present,” City said in a statement.
“The club wishes to thank the panel members for their diligence and the due process that they administered.”
Since Sheikh Mansour’s takeover 12 years ago, City’s fortunes have been transformed from perennially living in the shadow of local rivals Manchester United to winning four Premier League titles in the past eight years among 11 major trophies.
On Saturday, they secured qualification for the Champions League for a 10th consecutive season with a 5-0 win at Brighton.
More silverware could come before the end of the season as Guardiola’s side face Arsenal in the FA Cup semi-finals on Saturday before restarting their Champions League campaign in August, holding a 2-1 lead over Real Madrid from the first leg of their last 16 tie.
City’s victory in court will raise fresh questions over how effectively UEFA can police FFP.
But European football’s governing body said it remained committed to the system which limits clubs to not losing more than 30 million euros, with exceptions for some costs such as youth development and women’s teams, over a three-year period.
“UEFA notes that the CAS panel found that there was insufficient conclusive evidence to uphold all of the CFCB’s conclusions in this specific case and that many of the alleged breaches were time-barred due to the five-year time period foreseen in the UEFA regulations,” UEFA said in a statement.
“Over the last few years, Financial Fair Play has played a significant role in protecting clubs and helping them become financially sustainable and UEFA and ECA remain committed to its principles.”
