Emma Raducanu left the court in tears after retiring from her round of 16 match at the ASB Classic with an ankle injury just 11 days before the start of the Australian Open.
The British No. 1 was competing against Viktoria Kuzmova, with the score at 6-0, 5-7 when she appeared to turn her ankle.
The 20-year-old attempted to continue but was forced to withdraw just one point later, bursting into tears on court and exiting quickly.
"I've put a lot of physical work in the last few months and I've been feeling good and optimistic," Raducanu was quoted as saying by Stuff Media.
"So to be stopped by a freak injury, rolling an ankle is pretty disappointing, in the first week as well. I thought I was playing some pretty decent tennis.
"The courts are incredibly slick, like very slippery, so to be honest it's not a surprise that this happened to someone ... we'll assess over the next few days and see what the next steps are."
Raducanu ended her 2022 season in October due to a wrist injury, and said earlier this week that goals for 2023 were to "stay injury-free" and play "fearless" tennis.
This fresh injury raises concerns for the former US Open champion as the Australian Open gets underway in Melbourne on Jan. 16.
Information from Reuters contributed to this report.