Some FIFA rules on player transfers are contrary to European Union legislation relating to competition and freedom of movement, the EU's top court said on Friday.
The ruling will likely lead to a shakeup of the soccer market's global regulations and could change the sport's economy.
The European Court of Justice's ruling came after former France international Lassana Diarra legally challenged FIFA rules following a dispute with a club dating to a decade ago. Diarra argued that FIFA's restrictions meant he was unable to find a new club after his contract with Russian club Lokomotiv Moscow was terminated in 2014.
FIFA's rules state that if a player terminates his contract without ''just cause," the player and any club wishing to sign him are jointly liable for paying compensation to the previous club.
''Those rules hinder the free movement of players and competition between clubs,'' the court said in a statement. ''The rules in question are such as to impede the free movement of professional footballers wishing to develop their activity by going to work for a new club.''
The ruling is seen as crucial because it could make it easier for players to terminate their contracts and join another team — potentially leading to a scenario where bigger clubs could more easily poach players from smaller rivals.
The global players' union FIFPro, which supported Diarra's case, said the ruling ''will change the landscape of professional football.''
However, it could take a couple of years before any changes to the system go into effect as Friday's ruling is part of a Belgian court case that is still ongoing.