Super agent Jorge Mendes earned River Plate a massive €30m this week.
With Chelsea paying Enzo Fernandez's €120m buyout clause to ferry him away from Benfica, former club River took a 25 per cent cut of the fee as part of the original sale agreement.
And key to the windfall was Mendes, who offered advice to River when they were preparing to sell Fernandez last year.
Local journalist Juan Cortese revealed Mendes told River's board: "If Benfica comes to pick him up, don't sell him in full.
"Only sell a part [of the registration]. It keeps a percentage of a future sale, because they will surely sell him for more than 100 million euros."