The incident occurred on Wednesday afternoon as Accola was cutting a crop on his farm in Davos Platz in the canton of Graubünden, a cantonal government official confirmed.
Accola reportedly reversed his tractor into the path of the boy, who was crushed by the impact.
He was rushed by helicopter to the cantonal hospital in Chur by the Rega emergency service but succumbed to his injuries several hours later, cantonal police said.
An investigation into the tragedy has been launched, prosecutor Maurus Eckert said.
The Blick newspaper reports that Accola’s family expressed its condolences to the family of the boy.
Accola, 45, won seven World Cup skiing victories and clinched the overall World Cup in 1992.
He retired after almost two decades in the sport seven years ago.