Swiatek has won four French Opens, the US Open and Wimbledon, but a title at Melbourne Park has proved elusive.

Wawrinka, now ranked 139, peaked at world number three in 2014, winning the French Open a year later and the US Open in 2016.

"I've had to make the difficult decision to withdraw to address something my body needs attention for after my last match," said the 16th seed.

Players and spectators roasted on day seven at Melbourne Park, where temperatures soared to 38C.