Pumas UNAM burned off major European competition to sign Facundo Waller from Uruguay's Plaza Colonia.
Waller has joined Pumas on-loan for the season with the option to buy.
Manta was quoted by Mediaotiempo: “The important clubs scout and he had the best of the marks. What happens is that Benfica buy cheap and sell expensive and well, no agreement was reached, we believed that Facundo Waller was worth more than what they offered us and we went to Italy to be able to assert the price he was worth at that time.
"I was with Italian people and the business was practically closing, but in Uruguay he suffered an injury and that put off the Italians."
Manta added: "Coito, who was the coach of the Uruguayan team at that time, said that the most important player he had was him, he was not talking about (Rodrigo) Bentancur or (Fede) Valverde."
Pumas' permanent option is worth $2m.