Sporting Lisbon have reportedly filed a claim for Wolverhampton Wanderers to pay £40m for goalkeeper Rui Patricio.
Patricio has been involved in a dispute with Sporting since the end of the season, and the Portugal international opted to cancel his contract soon after a group of supporters attacked members of the first-team squad at the training ground.
However, according to A Bola, Sporting have opened legal proceedings seeking to receive the goalkeeper's release clause and the remaining value of his wages in his contract.
If successful, Wolves would be required to pay nearly £40m for Patricio - who has just represented his country at the World Cup - while another £8m would come from his personal terms.
Last week, Wolves suggested that they were prepared to hold discussions with Sporting regarding the transfer.