Football's player transfer system will be in the spotlight and could even be on the brink of collapse on Friday when the Court of Justice of the European Union (CJEU) announces its ruling on former France player Lassana Diarra's case against FIFA.

The international transfer system, which processes hundreds of millions of dollars each year in player sales and has existed in its current form since 2001, is overseen by world soccer's ruling body.

Diarra challenged it, however, when he successfully claimed in a Belgian court in 2017 that FIFA's transfer rules had blocked him from moving to a new club after his contract was terminated by Lokomotiv Moscow.

FIFA's regulations state that if a player breaches his contract, which is then terminated by the club, his new team is jointly liable with the player to pay compensation to his old one - which happened when Charleroi attempted to sign Diarra after his contract was ended by the Russian club in 2014.

FIFA refused to issue an International Transfer Certificate (ITC), effectively preventing Charleroi from registering Diarra with the Belgian federation.

In April 2015, FIFA's Dispute Resolution Chamber (DRC) ordered Diarra to pay 10 million euros ($11 million) to Lokomotiv Moscow.

Because the former Chelsea, Arsenal and Real Madrid midfielder was without a club, however, it ruled that any future employer would not be jointly liable to pay compensation and Diarra joined Olympique de Marseille.

New rules

The Court of Arbitration for Sport (CAS) rejected Diarra's appeal against FIFA's ruling but the player sued FIFA and the Royal Belgian Football Association in a Belgian court for damages and six million euros in loss of earnings since the clubs interested in signing him for the 2014-15 season had backed out because of the joint liability rule.

The Belgian court asked the CJEU for guidance, and the European Court's decision could be devastating for FIFA, if it follows the recommendation of Advocate General Maciej Szpunar to the judges, saying they should side with the player.

"Some FIFA rules on transfer of players may prove to be contrary to EU law. These rules are of restrictive nature and may only be justified in specific circumstances," he wrote in a non-binding opinion.

Diarra, who ended his career with Paris St Germain in 2019, is represented by Jean-Louis Dupont, the same lawyer who took the case of Belgian Jean-Marc Bosman, which in 1995 cleared the way for players in the European Union to move to other clubs at the end of contracts without a transfer fee being paid.

Dupont said this year that a judgment backing the footballer would be a milestone in modernising football governance in the bloc as it would allow players' unions and clubs' unions to regulate their employment practices.

"This will put an end to the degrading practice of commoditising players," lawyers Dupont and Martin Hissel said in a joint statement in April.

'Seismic'

It is still unclear how the ruling would impact countries beyond the EU, notably England's Premier League, the biggest source of transfer funds in the world, but it is likely to result in a new FIFA ruling that would be used in all member countries.

If there are fewer obstacles and deterrents to a player breaking contract, it follows that transfer fees could trend downwards if clubs feel they have less security in the event of an in-contract player walking away.

Contracts might also shorten if they become less stable.

A senior source within the European club game told PA the Diarra ruling had the potential to be a "dangerous one", adding: "The transfer market is the glue that holds the pyramid together.

"(The Diarra ruling) could have seismic implications, because if that glue starts to deteriorate, then that polarization (between the big leagues and the rest) will get worse."

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