World No 1 Aryna Sabalenka said she feels "disrespected" by tennis' governing body and claimed the hastily built court being used for the WTA Finals at the Mexican resort of Cancun is "not safe".
Sabalenka eased past Greece's Maria Sakkari 6-0, 6-1 in her group-stage opener on Sunday but that didn't prevent her from taking aim at the organisation.
"I have to say that I am very disappointed with the WTA and the experience so far at the WTA Finals," the 25-year-old from Belarus wrote on Instagram.
"As a player I feel disrespected by the WTA. I think most of us do. This is not the level of organisation we expect for the Finals.
"To be honest I don't feel safe moving on this court a lot of the time."
Sabalenka claimed players were not allowed to practice on the court until the day before the opening.
"It's just not acceptable to me with so much on the line and with so much at stake."
Cancun was only confirmed as the host city of the prestigious season-ending championship on September 7 after Saudi Arabia had reportedly been lined up to stage the event.
That possibility sparked criticism from US legends Martina Navratilova and Chris Evert among others.
Instead, the tournament has returned to Mexico for the second time in three years, after Guadalajara hosted in 2021.
Sabalenka said her criticism of the event was aimed at the WTA, not local organisers.
"I definitely want to show my appreciation for the local tournament organisers, everyone that built the court at the last minute, and everyone that's working here at the event," she wrote.
"I know it's not their fault."
On court on Sunday, Sabalenka, who captured this year's Australian Open title, fired six aces and 17 winners while saving all five break points she faced to dispatch Sakkari.
Sakkari saved three match points to hold serve in the penultimate game but fell after 74 minutes.
American Jessica Pegula defeated Kazakhstan's Elena Rybakina 7-5, 6-2 in 83 minutes in the other singles group stage match at the $9 million outdoor hardcourt showdown.
Two groups of four players will compete in round-robin matches through to Friday with the two top finishers in each group advancing to Saturday's semifinals. The final will be next Sunday.
Sabalenka is trying to hold off second-ranked Iga Swiatek, the reigning Roland Garros champion from Poland, to claim the year-end No 1 ranking.
Sabalenka can clinch the year-end top spot by going 2-1 in the group stage and reaching the final no matter what Swiatek does.
The triumph by Sabalenka ensures Swiatek must win the title to have a chance at the year-end top spot.
Sabalenka was the runner-up in the US Open and reached the semifinals at Wimbledon and Roland Garros. She also won WTA titles this year at Madrid and Adelaide.
She became world No 1 after her run to the US Open final in September, ending Swiatek's 75-week rankings reign.
Monday's opening matches in the other group send Swiatek against reigning Wimbledon champion Marketa Vondrousova of the Czech Republic and 19-year-old American Coco Gauff, the US Open champion, against Tunisia's Ons Jabeur.