Uefa has announced a formal investigation into the multi-million pound transfer window spending of Paris Saint- Germain, and whether it has complied with financial fair play (FFP) rules requiring clubs to break even.

The decision to investigate now, rather than wait for the normal retrospective look at clubs’ financial years which begins in March, follows widespread concern and complaints from Barcelona, Real Madrid and the Spanish league president Javier Tebas, that PSG are flouting the rules. The £198m signing of the Brazilian striker Neymar from Barcelona last month was by far the most paid for any footballer ever, and PSG followed that this week with a complicated £167m signing of the 18-year-old forward from Monaco, Kylian Mbappé.

In a statement, European football’s governing body said: “The Investigatory Chamber of the Uefa Club Financial Control Body has opened a formal investigation into Paris Saint-Germain as part of its ongoing monitoring of clubs under Financial Fair Play (FFP) regulations. The investigation will focus on the compliance of the club with the break-even requirement, particularly in light of its recent transfer activity. “

It is understood that a decision on whether PSG have breached the rules still cannot be taken until the end of the financial reporting period. But the Uefa committee has taken the unusual step of investigating in order to support the credibility of the FFP rules and monitor how PSG account for their mammoth spending. The committee will also be able to examine the means of funding the Mbappé signing, following reports that PSG will use an initial loan period, which will delay the actual payment to Monaco until the following financial year.

The FFP rules seek to discount any artificial means by which clubs meet the requirement to approach breaking even - currently losses are limited to €5m in total for the 2015-16, 2016-17 and 2017-18 periods, or €30m if an owner is entirely covering the extra €25m. Investment in youth development, a stadium and other infrastructure is allowed and offset against any loss greater than that.

The Uefa statement said the investigatory chamber “ will regularly meet in order to carefully evaluate all documentation pertaining to this case.”

Potential sanctions for a breach of FFP range from withholding Champions League prize money and reducing the size of a club’s squad, to the strongest measure of exclusion from the competition.

PSG, owned by the Qatar sovereign wealth fund QSI, has form for breaching FFP rules, having accepted a €60m reduction of prize money and a reduction in squad size in May 2014, after a previous Uefa investigation. PSG were considered then to have artificially inflated their income by means of a sponsorship deal with another state-owned enterprise, the Qatar Tourism Authority, reportedly for €200m a year. Uefa said that it had only accepted the Qatar Tourism Authority deal as income at a figure “significantly below that submitted by the club.” Some within Uefa are thought to have wanted to ban PSG from the Champions League then, but they were not a majority.

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In a statement, PSG said it was “surprised” by Uefa’s approach and was “very confident in its ability to demonstrate that it will fully comply with Financial Fair Play rules for the fiscal year 2017/2018.”

It said that it had already had exchanges with Uefa to demonstate how it would comply with FFP rules, highlighted the fact that it has “many high value” players under contract that it could sell to balance the books and anticipated an additional 20% to 40% uplift in revenues.