There's been a late change to Wednesday's schedule at the WTA Finals as Madison Keys was forced to pull out of the tournament ahead of her last round-robin match. The American went 0-2 in her first two matches of the week and had already been eliminated in the group stage, unable to advance to the semi-finals.

Keys was expected to face Elena Rybakina, who has already booked her spot in the semi-finals, in a dead-rubber match at 5pm local time (2pm UK). When the Aussie Open champion withdrew, first alternate Mirra Andreeva was expected to step in. However, she chose not to sign on as the alternate, and Ekaterina Alexandrova will now take Keys' place.

There's been an illness going around at the WTA Finals in Riyadh, with Keys feeling under the weather. After losing to Amanda Anisimova from a set and a break up on Monday, the No. 7 seed opted not to shake hands at the end of the match, telling Anisimova that she was unwell.

Keys also lost to Iga Swiatek in her opening match on Saturday, and her defeat to Anisimova meant that she would be unable to advance out of the group into the semi-finals, making Wednesday's match meaningless for her chances.

Hours before she was due to face Rybakina, the American pulled out of the season-ending finals. And she has been replaced by the second alternate, Alexandrova.

Andreeva narrowly missed out on the chance to qualify for her first WTA Finals singles event this year when she was overtaken by Rybakina. But she did not choose to enter the field as Keys' substitute, as she's also been feeling ill.

"Rybakina is playing Ekaterina Alexandrova. Madison Keys unfortunately too ill so isn't able to take to the court. Alexandrova is the second alternate because the first alternate, Mirra Andreeva, who is also in the doubles, is pretty under the weather," Gigi Salmon said on Sky Sports.

Andreeva herself seems to have picked up the illness going around this week. The Russian teenager qualified for the doubles event with her partner, Diana Shnaider, but they've lost their first two matches and have one round-robin tie left on Thursday.

Like Keys, Andreeva elected not to shake hands with her opponents after her second group match. Jasmine Paolini, who qualified for both singles and doubles at the WTA Finals, has also been feeling unwell.

The Italian has lost her first two singles round-robin matches to Aryna Sabalenka and Coco Gauff, and is due to face Jessica Pegula on Thursday.

However, she's had more success in the doubles draw with partner Sara Errani. They're the No. 1 seeds and won their opening match against Asia Muhammad and Demi Schuurs before losing to Su-Wei Hsieh and Jelena Ostapenko.

Paolini could also choose to withdraw ahead of her last singles match, as she cannot advance from the group stage to the semi-finals and may want to focus on doubles to conserve her energy. Should the Italian withdraw from her final singles match, Andreeva would be the only other alternate expected to take her place.

Meanwhile, Alexandrova will now turn her attention to her last-minute clash with Rybakina. They met in the recent Ningbo Open final, where Rybakina came back from a set down to win 3-6 6-0 6-2.

Earlier in the week, Alexandrova had been spotted in the stands taking in some of the action. She received a £114k appearance fee just for turning up and playing zero matches. Now that the world No. 10 has been called up for one match, she's set to bank £161k in appearance fees instead, plus there's £272k ($355k) up for grabs for every round-robin win.