City were fined 49 million pounds (US$63 million) and hit with restrictions on transfer spending and their Champions League squad after FFP breaches were originally investigated by football's European governing body in 2014.
UEFA launched a new round of investigation based on "leaked " internal City emails and other documents published by the German magazine Der Spiegel last November. The files appeared to unveil how City used direct funding from Abu Dhabi United Group, the investment fund owned by Sheik Mansour to supplement sponsorship deals. It is claimed that the Abu Dhabi United Group, which owns City, directly paid 59.5 million pounds (US$76.16 million) of Etihad's annual sponsorship, with only eight million pounds (US$10.24 million) coming from the airline company.
UEFA's rules place a strict limit on the capital an owner can inject directly into a club. City could be stung with a one-season ban from Champions League competition if they are found guilty of breaching FFP regulations.
UEFA introduced the Financial Fair Play (FFP) to stop clubs from getting stuck in severe debts or allowing wealthy sponsors to give their teams an unfair advantage.
"The Club Financial Control Body (CFCB) chief investigator, after having consulted with the other members of the independent investigatory chamber of the CFCB, has decided to refer Manchester City FC to the CFCB adjudicatory chamber following the conclusion of his investigation," said a UEFA statement.
"The CFCB investigatory chamber had opened an investigation into Manchester City FC on 7 March 2019 for potential breaches of Financial Fair Play (FFP) regulations that were made public in various media outlets."
City immediately responded, "The accusation of financial irregularities remains entirely false and the CFCB IC referral ignores a comprehensive body of irrefutable evidence provided by Manchester City FC to the Chamber."
"The decision (to refer the case) contains mistakes, misinterpretations and confusions fundamentally borne out of a basic lack of due process and there remain significant unresolved matters raised by Manchester City FC as part of what the club has found to be a wholly unsatisfactory, curtailed, and hostile process," the club added.
Sheikh Mansour bought the club in 2008, transforming the club from Premier League punchline into serial winners.
Paris Saint-Germain, backed by Qatari, have encountered a similar UEFA investigation for spending 400 million euros (US$449 million) to sign forward Neymar from Brazil and striker Kylian Mbappe from France.
The Court of Arbitration for Sport (CAS) backed the club against UEFA. Finally UEFA cleared PSG of wrongdoing.