INDIAN WELLS, Calif. (AP) — Karolina Muchova withdrew from the WTA Finals on Friday with a gastrointestinal illness.

The 30-year-old from the Czech Republic had been scheduled to play Mirra Andreeva on the last day of round-robin play in the season-ending championships.

Instead, second alternate Diana Shnaider of Russia stepped in to make her Finals debut in singles after qualifying in doubles last year with countrywoman Andreeva. They went 0-3 in round-robin play a year ago.

Muchova, a Wimbledon finalist this year, already lost her first two matches and could not have advanced to the semifinals even if she had played Friday.

Shnaider, however, had plenty of incentive. A victory over Andreeva would be worth $230,000 and 200 WTA Tour rankings points. She's also receiving a $220,000 participant fee.

Muchova is the second withdrawal of the eight-day, $10 million event at Indian Wells Tennis Garden. Top-ranked Elena Rybakina dropped out before the tournament began last Sunday, citing a viral illness and exhaustion.

It's the first time since 2019 that both singles alternates are competing in the round-robin stage. Marta Kostyuk replaced Rybakina and she went 0-3 in Group 1 play.

Advancing to Saturday's semifinals from Group 1 are Wimbledon champion Linda Noskova and American Jessica Pegula.

Andreeva already won Group 2 with a 2-0 match record regardless of Friday's result. The second spot will be decided by the result of a match between Aryna Sabalenka and Elina Svitolina.