Paris Saint-Germain has paid a quick price for its record-breaking investments in star forwards Neymar and Kylian Mbappe.

Uefa put Paris Saint-Germain's finances under formal investigation Friday (1 September), citing "recent transfer activity" that triggered concern the club was again flouting rules designed to control excessive spending by top European clubs.

Uefa's club finance monitoring panel intervened after Qatar-owned PSG broke the world-record fee to sign Neymar from Barcelona for €222m (£203.3m, $262m) and on Thursday signed AS Monaco forward Kylian Mbappe.

The deal for 18-year-old Mbappe was unusual as a loan with a commitment to pay a reported €180m next year.

That fueled speculation PSG was seeking to evade Uefa's monitoring of spending rules designed to ensure clubs try to break even on their football income and spending on player transfers and wages.

"The investigation will focus on the compliance of the club with the break-even requirement, particularly in light of its recent transfer activity," Uefa said in a statement.

The case has potential to embarrass a club owned by a Qatari sovereign wealth fund. It also suggests Uefa could be stricter with high-spending clubs under its president Aleksander Ceferin than his predecessor Michel Platini.

Uefa has power to bar clubs from the Champions League. Still, there is no suggestion PSG's place is at risk in the group stage which kicks off later this month.

However, the sale of other stars in the PSG squad now looks inevitable in the January trading window to placate Uefa's independent monitoring panel, and try to balance its books for the financial year.

"In the coming months, the Investigatory Chamber of the UEFA Club Financial Control Body will regularly meet in order to carefully evaluate all documentation pertaining to this case," Uefa said.

Uefa committed to Financial Fair Play eight years ago as a pet project of then-president Platini amid doubts that elite clubs would ever be severely punished. Platini's son, Laurent, taking a job closely tied to the Qatari ownership of PSG added to the skepticism.

In 2014, PSG and Abu Dhabi-owned Manchester City were the main targets of the first round of sanctions. Both had €20m of their Champions League prize money deducted and had limits imposed on their spending and squad size for matches.

Then, Uefa judges told PSG that a sponsorship deal with Qatar's tourism authority had been inflated above fair market value to help the club comply with the rules.

It was only in April that Uefa declared PSG had fulfilled its obligations of stricter ongoing scrutiny.

Weeks later, PSG began publicly pursuing Brazil star Neymar - for the second year running - to help regain the French league title from Monaco and become European champion for the first time. PSG has only once reached the Champions League semi-finals, in 1995.

PSG response

Responding to Uefa's announcement, PSG said they were "surprised" by the approach given that the club "constantly kept the Uefa Financial Fair Play teams informed about the financial impact of all players' operations carried out this summer, even though it wasn't obliged to do so". They added they were "very confident" in their ability to show that they will fully comply with FFP for the fiscal year 2017-18.

"The club reaffirms that it has always operated in total transparency with the European football bodies, with which it has developed trusted relationships over the last six years, demonstrating its upmost respect for the institution," PSG's official statement continued.

"In this respect, deputy CEO Jean-Claude Blanc met with Uefa experts including Andrea Traverso, responsible for Uefa Financial Fair Play, for more than three hours on August 23 at Paris Saint-Germain's headquarters, where he demonstrated that the operations carried out with FC Barcelona and in progress at that time with AS Monaco followed the rules of Financial Fair Play for the financial year 2017/2018.

"On 31st August, the club's general management again had exchanges with Uefa Financial Fair Play management to provide a more detailed account of how the transaction with AS Monaco would be integrated into the club's accounts for this season, in terms of amortization and payroll, in compliance with French accounting standards and IFRS.

"Furthermore, as for the summer of 2017, the club has already completed outgoing player transactions that helped improve club results by more than 104 million euros for the 2017/2018 season. The club also reminds, if necessary, that it has under contract many high valued players allowing the club to generate very significant capital gains in the next two transfer windows (January and June) of 2018.

"With the arrival of these two top players joining a high-quality team, the club is entering a new phase in its project to build a top-tier club and a world leading sports franchise. The club has demonstrated in recent years that it has the ability to grow its income exponentially and anticipates an additional 20 to 40% increase on all revenue streams available to the club (international revenue, sponsorships, merchandising, ticketing, TV rights, income related to sports results, summer and winter tours).

"In the interests of dialogue and transparency, the club will continue its exchanges with Uefa in the coming days and will respond, as it always has done, to each of the questions raised by the European body."

Paris Saint-Germain
Paris Saint-Germain broke the world transfer record earlier this summer Getty Images