The 18-year-old was involved in the accident in the early hours of Thursday morning, where firefighters tried to rescue Emilio near the Villas do Mar estate.
According to Portuguese TV channel TVI24, the tragedy happened in Troia, south of Lisbon, close to the house of Ballack, who retired as a professional footballer in 2012.
The quad-bike was designed to be used on public roads.
Emilio recently posted pictures of his time in Portugal at the weekend, showing pictures of his time at the beach with his family.
Details of his accident have not yet been disclosed.
Emilio Ballack (left), son of former Chelsea footballer Michael Ballack (right), has passed away
The 18-year-old was crushed by a quad-bike near the family's holiday home in Portugal, according to reports
Ballack is widely regarded as one of the best German players of all time and is a Premier League and FA Cup winner with Chelsea.
Ballack joined the Blues in 2006 after making his name at Bayer Leverkusen and Bayern Munich before spending four years at Stamford Bridge.
Emilio is one of three children of Germany legend Ballack, who married long-term girlfriend Simone Lambe in 2008.
More to follow
Ballack, pictured with sons Louis, Emilio and Jordi, at the World XI testimonial game at the Red Bull Arena in Leipzig in 2013
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Source : https://www.dailymail.co.uk/sport/sportsnews/article-9864747/Michael-Ballacks-son-Emilio-18-killed-quad-bike-crash-holiday-Portugal.html679