Sporting Lisbon president Bruno de Carvalho said that they had to sell Marcos Rojo to Manchester United following pressure from third-party owners.
According to the BBC, De Carvalho says third-party owners attended meetings, leading Sporting to think they were United officials.
He said that the club did not want Rojo, 24, to leave for he was an important player.
Carvalho added that the pressure was big as the third-party owners started to speak to the clubs and come for meetings.
Argentina World Cup defender Rojo who joined Sporting in 2012, signed for United in the summer for 16m pounds.
Third-party ownership (TPO) is banned in Britain, meaning any Premier League teams signing such players need to buy out any other parties, the report added.