River Plate are due a bumper 30m windfall from Benfica's sale of Enzo Fernandez to Chelsea.
In a statement announcing Fernandez's departure for London, Benfica detailed former club River's cut of the fee.
Benfica announced: "Sport Lisboa e Benfica Futebol, SAD has announced that it has reached an agreement with Chelsea FC for the transfer of all rights of the player Enzo Fernndez, for an amount of 121m.
"Benfica underline that Chelsea will have the right to withhold the 3.78% solidarity contribution to be distributed to the clubs that participated in the player's training.
"Benfica will also have to pay River Plate 25% of the transfer value deducted from solidarity charges and brokerage services."
