The two groups for this year's WTA Tour Championships in Istanbul have been announced.
Serena Williams has been drawn in the Red Group with world number one Victoria Azarenka, Angelique Kerber and Li Na.
The White Group is made up of Maria Sharapova, Agnieszka Radwanska, Petra Kvitova and Sara Errani.
The players will be involved in a round robin format, with the two best competitors from each group making it through to the semi-finals.
The end-of-season event starts on October 23.
