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.