The accident occurred early Thursday morning around 2am in the Portuguese town of Troia.
Emilio was 18 and is the second of Ballack’s three sons with former partner Simone Lambe, whom he wed in 2008 and divorced in 2012.
Emilio recently posted pictures of his holidays in Portugal on his social media handles over the weekend.
An officer based at Grandola near Troia said: “I know the dead man was the son of a well-known footballer but I don’t have details about who it was.
“The accident happened at the family home. The quad rider wasn’t on a public road and his was the only vehicle involved.
“The quad was on an uneven piece of land and at this stage it appears to have gone backwards and as it did fell on top of the victim and crushed him."
Jorge Santos, spokesman for the GNR police force in the city of Setubal, confirmed: “An 18-year-old man has died following an accident at a private property in Troia.
"We received an alert shortly after 2am this morning. I am not at liberty to go into details about the identity of the dead man.
“I can confirm he was on the vehicle he had his accident in alone.”
“The accident happened at a property on a residential estate called Vilas do Mar in Troia.
“The incident is now under investigation and there is nothing more we can say.”
Chelsea, where Ballack spent four years of his playing career, winning one Premier League, three FA Cups and one League Cup, tweeted a message of condolence to their former player which read: "Everybody associated with Chelsea Football Club is shocked and saddened to learn of the death of Emilio Ballack at the terribly young age of 18."
"All our thoughts are with his father Michael and his family at this sad time."
Ballack won 98 caps for the Germany national team, scoring 42 goals.
