Felix was sold by Chelsea this week to Al-Nassr for a fee rising to €50m. He joins the Saudis on a two-year deal worth €75m - net.
Saul, who canceled his Atleti contract to join Fla, told El Partidazo de Cope: "He has everything it takes to be a champion, but if you don't work hard, it's useless.
"We've tried many times to help him, but if someone doesn't want to… Talent without commitment isn't enough."
Meanwhile, on his choice to join Fla, Saul added: "The highest offer was from Trabzonspor, but I chose Rio for personal reasons. Filipe's presence on the bench was decisive: I have a special relationship with him.
"My story there (Atletico) was a bit strange, but I fulfilled my dream of playing for Atlético. I left a good impression at every club I've been to, and that's what matters."