La Liga has announced its intention to file a legal complaint against Paris Saint-Germain over Kylian Mbappe's "scandalous" new contract.
The 23-year-old was initially due to become a free agent at the end of the current season and was widely expected to sign for Real Madrid on a free transfer.
Los Blancos failed with a nine-figure offer in the final knockings of the summer transfer window last year, and Mbappe had supposedly already agreed personal terms with the club.
However, Mbappe stunned the footballing world by putting pen to paper on a new contract at PSG on Saturday, and the striker is now tied down to the French champions until 2025.
Mbappe's blockbuster new contract will reportedly see him earn a whopping €40m (£33.8m) per year, as well as having a high level of control over the club's commercial aspects.
News of Mbappe's new deal has not gone down well at all with those in Spain, though, and La Liga has announced its intention to write to UEFA and officially complain for threatening "the integrity of the sport".
"LaLiga wishes to state that this type of agreement attacks the economic stability of European football, putting at risk hundreds of thousands of jobs and the integrity of the sport, not only in European competitions, but also in domestic leagues," a statement read.
"It is scandalous that a club like PSG, which last season reported losses of more than €220m (£186m) after accumulating losses of more than €700m (£591.7m) in prior seasons (while reporting sponsorship income at doubtful valuation), with a squad cost around €650m (£549.4m) for this season, can close such an agreement, while those clubs that could afford the hiring of the player without seeing their wage bill compromised, are left without being able to sign him.
"LaLiga will file a complaint against PSG before UEFA, the French administrative and fiscal authorities and European Union authorities to continue to defend the economic ecosystem of European football and its sustainability."
The league also led an attack on PSG owner Nasser Al-Khelaifi, claiming that state-owned clubs such as the French champions have no respect for the rules of the game, and such behaviour is on par with the European Super League debacle.
"In the past LaLiga has complained to UEFA for non-compliance with financial fair play by PSG. These complaints were successful and UEFA sanctioned the club, while the Court of Arbitration for Sport (CAS), in a bizarre decision, reversed the sanctions.
"LaLiga and many European football institutions had hope that PSG President Nasser Al-Khelaifi after entering bodies of European football management such as the UEFA Executive Committee and the presidency of the European Club Association (ECA) would abstain from these practices knowing they cause grave damage, but the opposite has been true.
"PSG is assuming an impossible investment, seeing that it has an unacceptable wage bill and large financial losses in prior seasons. It is violating current UEFA and French economic control rules.
"This behaviour demonstrates once more that state owned clubs do not respect and do not want to respect the rules of a sector as important as football. These rules are key to protect and sustain hundreds of thousands of jobs.
"This kind of behaviour led by Al-Khelaifi, president of PSG, and member of the UEFA Executive Committee and president of ECA, endangers European football on the same level as the European Super League."
Mbappe celebrated his new contract in style on Saturday night, bagging a hat-trick on the final day of the Ligue 1 season against Metz, whose relegation was confirmed in that 5-0 thumping.
The 23-year-old also becomes the first player in Ligue 1 history to end the season top of the goals and assists charts, scoring 28 of his own while setting up a further 17 in PSG's title-winning campaign.