Kylian Mbappe has signed a new three-year contract with Paris Saint-Germain, but LaLiga has said it will file a complaint about the deal after he did not join Real Madrid.
The 23-year-old France international had been widely expected to leave the Ligue 1 champions for Real at the end of the season upon the expiry of his existing deal on June 30.
Real - who were willing to pay €230m to sign the forward on Deadline Day last summer - were ready to give Mbappe a signing-on fee of £110m and wages of £20m-a-year after tax. Their total investment would have been about £300m.
Mbappe was presented on the pitch ahead of PSG's Ligue 1 match at home to Metz - in which he scored a hat-trick - and said: "I would like to announce that I have chosen to extend my contract at Paris Saint-Germain, and of course I am delighted.
"I am convinced that here I can continue to grow at a club that provides everything necessary to perform at the highest level. I am also delighted to continue to play in France, the country where I was born, where I have grown up and where I have made my name."
Mbappe went on to score a hat-trick in the game against Metz as PSG ran out 5-0 winners at the Parc des Princes.
LaLiga furious with 'scandalous' deal
The news of Mbappe's U-turn was met with a vociferous response from Spanish football authorities, with LaLiga saying it will complain to UEFA, French tax authorities and the European Union over PSG's "non-compliance with UEFA's financial fair play".
A statement from LaLiga on Saturday night read: "This type of agreement attacks the economic sustainability of European football, putting at risk hundreds of thousands of jobs and sporting integrity at risk - not only in European competitions, but also in domestic leagues.
"It is scandalous a club like PSG, which last season reported losses of more than €220m, after accumulating losses of more than €700m in prior seasons (while reporting sponsorship income at a doubtful valuation) with a cost of sports staff around €650m for this 2021-22 season, can face an agreement of these characteristics while those clubs that could accept the arrival of the player without seeing their wage bill compromised, are left without being able to sign him.
"For all of the above, LaLiga is going to file a complaint against PSG before UEFA, administrative and tax authorities in France and before the competent bodies of the European Union, to continue defending the economic ecosystem of European football and its sustainability."
The statement concluded the behaviour of PSG president Nasser Al-Khelaifi and his club "endangers European football on the same level as the European Super League".
'PSG won't lose sleep over LaLiga legal action'
French football expert Tom Williams:
"I don't think I've ever seen a rival championship taking umbrage at a player signing a new contract at his club in another championship. I'm not a legal expect but I struggle to see how LaLiga can possibly affect this.
"It's not the first time [LaLiga president] Javier Tebas has been sounding off about the money PSG have and the way they spend it. It is obviously a lot of money that they're having to spend to hold onto Mbappe and question marks will be raised about that.
"As happy as PSG are, is it a great thing for football that this very small handful of clubs have the means they have and are able to spend money like that? It certainly doesn't feel like a good thing for the long-term health of the game.
"In terms of the suggestions of legal action from LaLiga or anything like that I suspect the PSG directors won't be losing too much sleep."
Mbappe mentioned the president in his statement announcing the contract: "I would like to thank the President, Nasser Al-Khelaifi, for his trust, his understanding and his patience.
"I would also like to thank all the fans of Paris Saint-Germain, both in France and around the world, for their support, especially in recent months. Together, side by side and ambitious, we will make magic in Paris."
'Amazing milestone' in PSG's history
Mbappe becomes the highest-paid player in world football on wages of around £1m a week after pocketing a signing-on fee in the region of £100m from PSG. The club have also made concessions over image rights with Mbappe in line to receive bonus payments for goals, Ballon d'Or honours and Champions League success.
PSG chairman and CEO Al-Khelaifi said: "Kylian's commitment to PSG represents an amazing milestone in the history of our club, and a wonderful moment for our fans around the world.
"Since the day Kylian joined our family, he has achieved greatness beyond his years on every single stage. In committing to PSG, he will be the foundation of our club's future both on and off the field.
"I am incredibly proud and very happy - for Kylian, for our fans, and our entire PSG family worldwide - that we will continue our wonderful journey together. For our fans and our club, the greatest chapters of our future lie ahead."
There remain big question marks over the future of PSG head coach Mauricio Pochettino and sporting director Leonardo. PSG want Zinedine Zidane to replace Pochettino this summer.
Why has Mbappe chosen to stay at PSG?
French football expert Jonathan Johnson:
"Money is obviously going to be a big motivating factor, but let's face it, Mbappe would have been well paid at Real Madrid as well.
"You have to look at the sporting aspects of the PSG project; they still haven't won this Champions League title they have been chasing for 10 years or more. It would also be a massive boost for the French game were Mbappe to be the key player for PSG when they bring home what would be just the second-ever Champions League success in France's history.
"This is also a massive boost for Ligue 1 at a time when it is desperately trying to salvage itself after the impact of Covid and trying to keep pace with the top five in Europe before the Champions League reforms come in.
"It's a big boost for PSG and Ligue 1, but also Mbappe. It's a challenge for him to be the difference-maker, the guy that turns PSG from perennial Champions League contenders to getting over the line."
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