Forestieri received a yellow card in Watford's 2-1 victory at Charlton Athletic on Tuesday that contributed to his sending-off, but Zola has revealed that he does not believe that Forestieri is guilty of simulation.
Zola told BBC Counties Radio: "He is quicker and that is why people think that he dives, but he doesn't.
"I have told him that he is not going to play if I find out he is diving.
"I don't like that. We want to win games in a different way."
Forestieri is one of 10 players that joined Watford in the summer on loan from Italian club Udinese.