Former US Open champion Emma Raducanu pulled out of the Auckland Classic on Tuesday with a "back niggle" in a blow to her Australian Open preparations.
Britain's Raducanu will now fly to Melbourne to begin rehabilitation ahead of the year's first major starting on January 12.
The 22-year-old has suffered a series of injuries since bursting onto the scene with her New York triumph in 2021.
"I've tried my best to be ready. I love Auckland and the fans here," the 56th-ranked Raducanu said.
"But unfortunately I've picked up a back niggle and I won't be ready in time."
Raducanu is travelling with renowned fitness coach Yutaka Nakamura in an attempt to better withstand the rigours of professional tennis.
Raducanu missed a chunk of 2023 following wrist and ankle surgery, and was recently sidelined for two months by a foot injury.
Former Australian Open semifinalist Elise Mertens also withdrew Tuesday hours before the second seed's first-round match in Auckland.
Top seed Madison Keys defied blustery conditions to win her first-round match in straight sets over Lucia Bronzetti.
American world number 21 Keys was relieved to start her season with a solid 6-4, 6-4 outing against the Italian.
"I feel like we all come out, we're a little bit nervous, but it's obviously so much fun to be back out here," she said.
"Lucia is one of those players who's just going to make you keep on having to play shots. So it's great for the confidence this early in the season."
The 29-year-old will next play unseeded Romanian Jaqueline Cristian after her Ukrainian opponent Yuliia Starodubtseva retired during their second set.
Former Australian Open champion Sofia Kenin beat China's Wang Xiyu 7-6 (7/5), 6-1, the American setting up a second-round match