FIFA has confirmed an investigation is underway after Sporting CP complained about Rui Patricio's transfer to Premier League new boys Wolves.
The Portugal international signed a four-year deal at Molineux last month after terminating his Sporting contract in the aftermath of an attack by a section of the club's supporters following their failure to qualify for the Champions League.
Sporting, who have opened legal proceedings against Patricio and six other players, remain angry at the free transfer and have written to FIFA to demand compensation.
The letter, published by Record, states Sporting are seeking €58.7 million (£51.8m/$65.5m) from Wolves, while also requesting the club are handed a transfer ban and Patricio is suspended for six months.
Football's governing body verified receipt of the dossier from Sporting and advised a full investigation was now underway.
"We can confirm that we have received a complaint from Sporting Clube de Portugal against Wolverhampton Wanders and the player [Patricio]," a FIFA spokesperson told Omnisport.
"As the contractual dispute is currently under investigation, please understand that no further comment can be made at this stage."
When contacted by Omnisport, Wolves declined to comment on the case.