UNITED NATIONS - World’s top ranked tennis player Novak Djokovic Thursday appointed goodwill ambassador by the United Nations Children’s Fund (UNICEF), after having served as the agency’s Serbia Ambassador and promoting children’s rights within his own private foundation. “Novak Djokovic is a true champion for children around the world. He has shown that a powerful voice and powerful actions can make a difference for children, especially when they are very young,” UNICEF Deputy Executive Director Yoka Brandt said in New York.