The Valencia striker's father, Antonio, admits his son made a massive mistake in joining West Ham last summer, and says the British weather and Slaven Bilic's tactics were to blame for his son's dismal spell at the London Stadium.
The Italian international joined Slaven Bilic's side last summer on a season-long loan deal from Juventus after Euro 2016, where Zaza was widely slated for his infamous penalty miss against Germany in the quarter finals.
His fortunes in London did not prove any better, as he made just 11 appearances in all competitions for the Hammers and failed to find the back of the net before his loan deal was cut short in January 2017.
He then spent the second half of the season on loan at Valencia, a move which has since been made permanent after an impressive return to form and his father, who is also his agent, has spoken about his wretched stay in the Premier League.
"It was a huge mistake,' Antonio told 'Calcio Mercato', talking about about his son's move to West Ham.
"Simone was still concerned by the penalty he missed with Italy at the time and he failed to settle in well in London.
"He was not happy with the weather and with the formation of his ex-boss. Moving to Spain was the best ever decision for him."
Zaza and his current club Valencia have enjoyed an excellent start to the season in Spain, as Marcelino's side remain unbeaten and the Italian striker has six goals in his first seven league appearances.
Despite this great run of form, Zaza was overlooked by Gian Piero Ventura in the latest Italy squad for the final two World Cup qualifiers, and Antonio admits his son is disappointed with the decision, and hopes his mistake at Euro 2016 won't ruin his future international career.
"We respect the choices of Ventura," he said. "Of course Simone was not happy for the decision because things are going well in Valencia at the moment, every player dreams of the national team.
"Only the ones who take the penalties miss them. When he took the responsibility he knew he could fail. I hope no (that the miss will count against him), anyway. He did many positive games with Italy."