Ekaterina Alexandrova has been called up to replace Keys after Mirra Andreeva, who holds world No 9, chose not to sign in due to lacking fitness to play in today's matches, according to the Women's Tennis Association.
Recent reports have highlighted issues about how competitors are being let down by the WTA.
Greetings to another day at the WTA Finals. Although both matches offer thrilling action, the main event showcases Iga Swiatek facing off with Anisimova.
Their previous encounter at Wimbledon four months ago was remarkably one-sided, with Swiatek achieving a commanding 6-0, 6-0 win. However, the American player delivered a remarkable comeback shortly after, defeating Swiatek in convincing fashion during the New York tournament.
Today's match represents the third chapter of their ongoing battle, with the winner progressing to the semi-finals in Riyadh.
Earlier in the day, Rybakina will face Alexandrova instead of the originally scheduled opponent. Keys withdrew due to illness in what represents a meaningless match, allowing the world No 10 to participate. Rybakina aims to maintain her perfect streak, having already beaten both her Polish rival and Anisimova to secure her semi-final position.
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