Manchester City are being investigated by Uefa for alleged financial fair play violations.
Uefa said the investigation "will focus on several alleged violations of FFP that were recently made public in various media outlets".
German news magazine Der Spiegel has published a series of claims, based on leaked documents, that Premier League champions City have violated FFP rules.
City said: "The accusation of financial irregularities is entirely false."
The club added: "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 club's published accounts are full and complete and a matter of legal and regulatory record."
FFP rules are designed to ensure the amount clubs spend on their players and wages is approximately equal to what they earn in commercial revenue and prize money.
Uefa previously found City had breached FFP rules in 2014.
The two parties reached a settlement, with City paying a £49m fine - £32m of which was suspended - while their Champions League squad was reduced for the 2014-15 season.
The Football Association is looking into claims City made a banned £200,000 payment to Jadon Sancho's agent when the England winger was 14 years old.
That allegation was also made in documents published by Der Spiegel last month.
Uefa says it will make no further comment while the investigation is ongoing.
In November, Der Spiegel alleged City had "deceived" European football's governing body.
It claimed City and their sponsors manipulated contracts to wipe out a £9.9m shortfall in 2013 and circumvent FFP regulations.
After those claims, Uefa said it would reopen FFP investigations on a "on a case-by-case basis" if there is evidence of "abuse".
In December, there were reports that City could be banned from European competition if Uefa found they had contravened FFP rules.
City manager Pep Guardiola subsequently said he had been assured by chairman Khaldoon al-Mubarak and chief executive Ferran Soriano that the club would not be banned.
However, in January, Uefa's chief FFP investigator Yves Leterme said City could face a Champions League ban if the claims are proven.
BBC sports news correspondent Richard Conway
The credibility of Uefa's financial fair play rules are on the line here.
They must be seen to be taking seriously these allegations of financial irregularities.
City firmly deny any wrongdoing.
But they - and Uefa - know that a lot is at stake. The European confederation has, ultimately, the power to bar City from the Champions League.
If it comes to that City - with the monetary and legal firepower of Sheikh Mansour behind them - can be expected to fight such a sanction tooth and nail.
This matter has a long way to go.