Casey Dellacqua has been forced to withdraw from the Australian summer of tennis due to lingering effects from concussion.
The 30-year-old, who enjoyed a break-out doubles season reaching two grand slam finals, fell heavily at October's China Open.
She was hospitalised and returned to Australia for treatment, hopeful of a quick recovery.
However, the West Australian has been diagnosed with Post-Concussion Syndrome, putting her playing future in doubt.
"Casey is still experiencing headaches, neck pain and is still not in a position where she is able to train to the level required to be able to play professional tennis," manager Sam Maxwell said.
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"There is no timeline on Casey's return at present, however we expect her to return to light training in the coming weeks with a return to the tour some time after the Australian summer."
She will miss the Australian Open, Hopman Cup mixed-teams event - where she was to have partnered Lleyton Hewitt in one of his farewell events - and the Sydney International.
Dellacqua said she was focused on making a full recovery.
"I'm really upset that I have to miss the whole Australian summer, but my health is my priority," she said.
"I am making small improvements each day and am looking forward to getting back on the tennis court again soon."
Dellacqua's doubles year brought a nomination for the John Newcombe Medal, won by Sam Groth.
She will be replaced at the Hopman Cup by Jarmila Gajdosova.
