Petkovic shares tale of friend's fight with cancer

Andrea Petkovic sat down with the WTA to talk about her friend Jonathan "Johnny" Heimes. They grew up playing together at the same tennis facility in Germany, and both were standouts pegged for making it on the pro tour.

But when Heimes was still very young, he began to lose his coordination skills and, by 14, he was diagnosed with a genetic dysfunction that was predisposed to cancer. Cancer would ultimately keep him off the court and take his life in 2016.

But through his battle, he carried a champion's mentality. A text from a friend reading "4: 6, 4: 5, 15:40. Two match balls against you. YOU HAVE TO FIGHT! Nothing is lost yet," inspired him to keep going. In 2015, he would start a non-profit organization with with the help of his friends, and in particular, Petkovic.

His non-profit Du Musst Kampfen (You Have to Fight) raises donations for supportive sports therapy for children with cancer at the University Hospital Frankfurt.