Some of Fifa's rules on player transfers may breach European Union regulations as they interfere with the contractual relations between players and clubs, an adviser to Europe's top court has said.

Advocate General Maciej Szpunar told the Court of Justice of the European Union (CJEU) that certain rules "are of restrictive nature and may only be justified in specific circumstances".

He added the rules can limit a club's ability to buy players and they can hinder competition in the transfer market.

The case has been brought to the CJEU by former Premier League player Lassana Diarra, who signed for Lokomotiv Moscow in 2013 but had his contract terminated a year later.

Former Chelsea, Arsenal and Portsmouth midfielder Diarra claims a move to Belgian club Charleroi collapsed because they were worried about having to pay compensation to Lokomotiv under Fifa's rules.

Diarra said football's world governing body's rules that a new club would be held jointly liable with him for paying compensation to Lokomotiv hampered his efforts to find another team.

He later sued Fifa and the Royal Belgian Football Association in a Belgian court for damages and six million euros (£5.1m).

The Belgian court asked the CJEU for guidance and Szpunar, plus Diarra's lawyers, have recommend the judges side with the player when the CJEU makes its ruling in the coming months.

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