Emilio Ballack, the son of former Germany and Chelsea midfielder Michael Ballack, has died at the age of 18.

Emilio Ballack was involved in a quad-bike accident which police told Reuters took place in the early hours of Thursday morning south of Lisbon.

Michael Ballack's former clubs Chelsea, Bayern Munich and Bayer Leverkusen sent messages of condolence to the family.

Oliver Kahn, who played alongside him for Germany and Bayern Munich, said he was "shook deeply" by the news.

"There are no words at a time like this," Khan said in a statement on Bayern Munich's website.

Chelsea, where Ballack won the Premier League title, League Cup and FA Cup three times, said they were "shocked and saddened" to learn of Emilio's death.