Uefa has informed Qatar-owned Paris Saint-Germain they may face sanctions for breaches of financial fair play rules, relating to huge deals with Qatari sponsors which a preliminary investigation has found to be excessive.

The deals, in particular a sponsorship of PSG by the Qatar Tourism Authority thought to be paying €120m annually, have been assessed for Uefa by an independent marketing consultancy as far above genuine commercial “fair value”.

The formal investigation into PSG’s finances was begun following last summer’s transfer window in which the club spent £198m signing the Brazil striker Neymar, followed by a loan deal with an option to sign the French forward Kylian Mbappé, valued at £167m.

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Around European football there were widespread complaints PSG must have been breaching FFP rules, which are aimed at restraining the growth in players’ wages by requiring Europe’s clubs to spend within their income and not make huge losses. Javier Tebas, the president of La Liga, accused PSG of financial doping and “peeing in the swimming pool” and promised to formally complain to Uefa. Tebas also accused Manchester City, owned by Sheikh Mansour of Abu Dhabi’s ruling family, of similarly receiving excessive money from Abu Dhabi sponsorships. City, though, did not face an accelerated investigation, and their “related party” sponsorships are thought not to be on the same scale as PSG’s with the QTA.

In this second phase of FFP’s implementation, losses are restricted to €30m over three seasons, with extra expenditure allowed for investment in sustainable areas including stadium development and youth academies. Money paid in by owners is not treated as income, as Uefa decided it is not a stable way for clubs to be financed, and too many were falling into financial difficulties in the 2000s. Crucially, owners cannot disguise their funding by paying money in other ways, so if sponsors are “related parties” to the owners, the value of the sponsorships is assessed to be sure it is a fair value, market price.

PSG, bought by Qatar Sports Investments in 2011, announced their first deal with the Qatar Tourism Authority shortly before its accounts were assessed by Uefa last time. Following an investigation in 2014, Uefa’s club financial control body (CFCB) agreed a settlement with sanctions against PSG, having determined the fair value of the QTA sponsorship was “significantly below that submitted by the club”.

This time the CFCB’s “investigatory chamber” commissioned a prominent independent marketing company, Octagon, to value the current QTA deal.

Octagon are understood to have assessed the deal’s benefit to the QTA is very much less than the money the QTA is paying PSG. So PSG faces sanctions and Uefa a very public test of its robustness in applying its FFP rules.

The club are understood to have commissioned their own independent valuation, and to be arguing the sponsorships are fair value, given the increased profile generated by the Neymar and Mbappé signings.

A spokesman said Uefa does not comment on ongoing investigations, but confirmed the investigatory chamber will meet on 20 April, although a final decision on PSG is unlikely then.