Manchester City are the subject of a UEFA investigation over a potential breach of Financial Fair Play (FFP) regulations.
European football's governing body announced on Thursday they have opened a formal investigation into the Premier League champions' financial conduct amid a number of alleged recently-reported violations.
A UEFA statement read: "UEFA Club Financial Control Body opens investigation into Manchester City for alleged Financial Fair Play violations.
"The Investigatory Chamber of the independent UEFA Club Financial Control Body has today opened a formal investigation into Manchester City FC for potential breaches of Financial Fair Play (FFP) regulations.
"The investigation will focus on several alleged violations of FFP that were recently made public in various media outlets."
UEFA had been looking into allegations published in the Football Leaks series by German magazine Der Spiegel that City systematically broke Financial Fair Play rules.
The revelations suggest City officials deceived UEFA over several years, including by disguising the source of revenue from sponsorship deals tied to the club's owners in Abu Dhabi. The magazine also alleged City hid payments to former manager Roberto Mancini and artificially reduced their image-rights costs.
City have repeatedly declined to address specific allegations, and have not contested the authenticity of the documents.
But the club responded to UEFA's announcement on Thursday, saying: "Manchester City welcomes the opening of a formal UEFA investigation as an opportunity to bring to an end the speculation resulting from the illegal hacking and out of context publication of City emails.
"The accusation of financial irregularities are entirely false. The club's published accounts are full and complete and a matter of legal and regulatory record."
At the turn of the year UEFA's chief FFP investigator and former Belgium Prime Minister Yves Leterme said: "If what has been written about Manchester City is true, there might be a serious problem.
"This can lead to the heaviest punishment - exclusion from UEFA competitions."
UEFA gave no timetable for the case, stating it "will make no further comments on the matter while the investigation is ongoing."