Boris Becker says constructive criticism helped Novak Djokovic's resurgence.
World No. 1 on concerns about playing New York.
The event in Belgrade plans to sell another 1,000 tickets to the public.
The Ultimate Tennis Showdown has added a pair of Top 10 players to its lineup, with one more big name expected to be added.
The 16-year-old spoke from the heart. She is becoming a source of inspiration for young people everywhere.
"If you ask me today if I want to travel to play a tennis tournament, I will say no," says Rafa Nadal.
The Italian is hoping to solve a problem that has plagued his ankles for nearly four years.
