The 29-year-old was set to play a key role in singles and doubles in Australia's Billie Jean King Cup qualification tie against Mexico in Brisbane from Friday.
But disaster struck in Thursday's final practice session, when the Rockhampton product collapsed to the surface of Pat Rafter Arena and grabbed at her right ankle.
Hunter was assisted off the court and sent for scans on Thursday night, confirming the bad news on Friday in a social media post before arriving at the venue to support the team.
"I am devastated and heartbroken but incredibly grateful to be around the team and I know I have a great group of people around me that will help me get back on court as soon as possible," she said.
"Thank you so much everyone for the messages of support and love, I'm excited to stay for the tie and support our Aussie girls."
The year-ending world No.1 in doubles was the feel-good story of the Australian Open in January when she surged from qualifying to make the third round at Melbourne Park.
Her good form continued, taking Hunter to a career-high singles mark of 114, and she was pushing Cup teammates Daria Saville and Arina Rodionova in the battle to be Australia's highest-ranked women's singles player.
Recovery time from achilles ruptures is at least four months but can take up toa year.
Hunter is helped off Pat Rafter Arena after rupturing her achilles on Thursday. (HANDOUT/TENNIS AUSTRALIA)
July's Olympics - at which Hunter loomed as a strong medal chance in women's and mixed doubles - is almost certainly off the table, with a long absence also likely from the WTA Tour.
"She's heartbroken," teammate Rodionova said after her first-rubber win put Australia ahead 1-0 in the tie.
"She really wanted to play here but also the upcoming few months; it's going to be tough.
"We all cried several times (after the injury). It's such a heavy thing; your teammate, a day before the tie. It was a lot.
"We tried to play for her and asked her to stay with us, so (we could) support her.
"When you get injured like that you kind of feel nobody really cares about you, but it's not like that.
"If we win, we all win."
An injured Storm Hunter puts on a brave face while watching Australia from the stands in Brisbane. (Darren England/AAP PHOTOS)
It isn't the Queenslander's first setback, after injury forced Hunter to give up singles for almost two years in her mid-20s.
She had been eagerly anticipating a return to her home state as Australia hosts its first Cup tie since 2019.
"When they did the draw it was like, 'Please be at home'," she told AAP earlier this month.
"It's the dream and I haven't had that opportunity, only being around the team in recent years.
"My level's higher than I thought it was and the sky is the limit now."
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