De Visser first spotted Firmino when the striker was playing in Brazil, but was unconvinced.
"I saw Firmino at Figueirense, a club of nothing," he told FOX Sports. "The man who managed him said, 'Piet, that's him'.
"And I didn't see it, I'm honest about that. Now I think he's a fantastic striker, that's what happens. "
"He just wasn't good at the time," De Visser says. "You also sometimes see one that is top in his younger years, but he just doesn't make it."