Stan Wawrinka’s comeback tournament ended with a second-round loss to Tennys Sandgren at the Australian Open.
The 2014 champion was back in action for the first time since Wimbledon after undergoing surgery on his left knee.
He never looked comfortable against American Sandgren, ranked 97, and lost comprehensively 6-2, 6-1, 6-4.
Of more concern was the degree of pain Wawrinka seemed to be feeling in his knee, with the 32-year-old wincing and flexing the joint, which bears a large scar.
There was a smoother ride for defending champion Roger Federer, who fought off the challenge of Jan-Lennard Struff to move into the third round with a comfortable 6-4, 6-4, 7-6 (7/4) win.
Earlier in the day Novak Djokovic overcame Gael Monfils in brutal conditions at a sun-baked Rod Laver Arena.
The thermometer headed towards 40°C in the shade and the heat began to take a serious toll on the Frenchman, who appeared to consider retiring before eventually going down 4-6, 6-3, 6-1, 6-3.