BRUSSELS - Some of the world soccer governing body FIFA's rules on player transfers may breach EU rules as they hamper players seeking to move to another team and clubs looking to hire players, an adviser to Europe's top court said on Tuesday.

The case before the Luxembourg-based Court of Justice of the European Union centered on former French professional footballer Lassana Diarra, 39, who challenged the rules governing contractual relations between players and clubs.

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Diarra had signed for Russian football club Lokomotiv Moscow in 2013 but his contract was terminated a year later for an alleged breach. Lokomotiv then applied to the FIFA Dispute Resolution Chamber for compensation and the player counterclaimed for unpaid wages.

Diarra's lawyer said a judgment backing the footballer would be a milestone in modernizing football governance in the bloc as it would allow players' unions and clubs' unions to regulate their employment practices

The player said FIFA rules that a new club would be held jointly liable with him for paying compensation to Lokomotiv hindered his efforts to find another team.

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He subsequently sued FIFA and the Royal Belgian Football Association in a Belgian court for damages and six million euros ($6.43 million) in loss of earnings. The Belgian court then asked the CJEU for guidance.

Diarra, who made more than 30 appearances for France, later played for club sides Olympique de Marseille, Al Jazira and Paris St Germain before retiring in 2019.

Advocate General Maciej Szpunar at the CJEU said judges should side with the player.

"Some FIFA rules on the 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.

He said the rules limit clubs' ability to recruit players and affect competition between clubs on the market for the acquisition of professional players.

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The CJEU, which will rule in the coming months, usually follows the majority of such recommendations.

Diarra's lawyer said a judgment backing the footballer would be a milestone in modernizing 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 commoditizing players," lawyers Jean-Louis Dupont and Martin Hissel said in a joint statement.