Sporting Lisbon have reportedly inserted a £43m buyout clause in Bryan Ruiz's contract following his transfer from Fulham.
The Costa Rica international has moved to the Portuguese side on a three-year contract from Craven Cottage.
The 29-year-old joined Fulham from FC Twente for £10.6m in 2011 and went on to make 106 appearances for the West London outfit.
According to the London Evening Standard, Sporting have inserted the high buyout clause into Ruiz's contract to protect them from interest in him, which is common practice in Portugal.
Ruiz played 32 times in the Championship for Fulham last season.