The former world number one overcame fellow Spaniard Carla Suarez Navarro 6-3 6-4 on Monday and was due to face seventh seed Kiki Bertens in the second round, but event organisers confirmed the Dutch player had been given a walkover to the last eight.
WTA Sydney
Kvitova overcomes Barty to take Sydney International title
12/01/2019 AT 09:13
With the draw for the Australian Open due to take place on Thursday ahead of the opening day of the year's first Grand Slam in Melbourne on Monday, 25-year-old Muguruza will be mindful of her physical condition.
She damaged a thigh muscle during the Hopman Cup in Perth last week, prompting her withdrawal from a mixed doubles match with France.
The former French Open and Wimbledon champion has dropped to 18 in the world over the past year, and is an 18-1 outsider with bookmakers for a third Grand Slam this month.
Her best performance at the Australian Open was a quarter-final appearance two years ago when she lost in straight sets to Coco Vandeweghe.
WTA Sydney
Halep stunned by Barty in Sydney second round
09/01/2019 AT 05:54
WTA Sydney
Kerber swats aside Giorgi to reach Sydney quarter-finals
08/01/2019 AT 11:55