Firmino had trials with OM in 2009, but eventually signed for Hoffenheim.
Durand said: "He arrived through our network of informants we have in Brazil. He was proposed to us. He seemed interesting to us.
"We had him come for a month in Marseille, he trained with the reserve team. All the educators were unanimous, he was an interesting player. After he did not sign with us. He was a minor. Technically, in his way of playing, we saw that he was of a higher level. After that he was a kid.
"After, at the time, in the recruitment strategy of OM, it was not validated to put money on a player like that. It was definitely a mistake."