Sporting Lisbon have lodged a formal complaint to FIFA regarding the transfer of goalkeeper Rui Patricio to Wolverhampton Wanderers.
Patricio was one of nine players to cancel their contract at Sporting last season following an attack by the club's own fans at their training ground just days before they were due to play in the Portuguese cup final.
The 30-year-old subsequently joined newly-promoted Wolves on a free transfer, although Sporting are understood to want £48m in compensation for the player.
BBC Sport reports that FIFA has now received an official complaint against both Wolves and Patricio over the deal, which is understood to have also involved agent Jorge Mendes.
Patricio, who was Portugal's number one at this summer's World Cup, spent 18 years at Sporting, making 467 appearances for the first team.
