World number one and defending champion Elena Rybakina has withdrawn from the WTA Finals in Indian Wells, with Ukraine’s Marta Kostyuk taking her place in the eight-player field, Al Jazeera reported.

Organisers cited a viral illness on Saturday. Rybakina said she was not physically ready to compete, while tournament director Garbine Muguruza said the Kazakh player had been unable to recover in time after physical problems late in the season.

“I spoke to her today, and she really couldn’t recover on time,” Muguruza told Reuters in comments carried by Al Jazeera. “We don’t want her to feel like she has to play — only if she’s ready to.”

Rybakina also withdrew from the quarterfinals of the Pan Pacific Open in Tokyo last month because of a neck injury.

Kostyuk was already in Indian Wells as an alternate and was practising when the withdrawal came. She will make her WTA Finals debut after a season that included the Madrid title and a rise into the top 10.

Rybakina’s absence could give world number two Aryna Sabalenka an opportunity to narrow the rankings gap, Muguruza said.

The tournament was moved from Riyadh, Saudi Arabia, to Indian Wells, California. Muguruza said player safety amid conflict in the Middle East was the decisive reason for the relocation.

Sources