The decision was made by Portugal's Court of Arbitration for Sport (TAS) after the Primeira Liga side originally sought €45 million in damages, per ESPN UK's Adriana Garcia.
Leao, now 20, was one of nine Sporting players who nullified their contracts after a group of 40 fans broke into the club's training center in May 2018, attacking players and staff amid a tumultuous spell for the 18-time Portuguese champs.
Current Wolves pair Rui Patricio and Daniel Podence, and Real Betis midfielder William Carvalho were also among the nine who terminated their deals following the melee that injured now-Eintracht Frankfurt striker Bas Dost.
Sporting initially approached the Court of Arbitration for Sport (CAS) to appeal FIFA's ruling that prohibited the club from getting compensation for Leao and then-teammate Ruben Ribeiro's unilateral contract annulments.
Sporting's market regulator confirmed the TAS decision Thursday, citing Leao's "unlawful termination of the sports employment contract."
Leao is eligible to appeal the ruling.