The Italian has withdrawn from the ATP Finals due to an abdominal injury.
The American legend has the highest praise for Novak Djokovic.
The WTA Finals will feature a Spanish finalist for the first time since 1993.
"Being No. 1 in the world, there is no reason for me yet to think about leaving tennis," says Novak Djokovic.
The Canadian is the second ATP player born in the 2000s to crack the milestone.
"I think the Australian Open is not a real possibility right now," Roger Federer's coach, Ivan Ljubcic, said.
The WTA chief tells Chris Clarey of the New York Times that the tour is fully behind Peng Shuai
