Nick Kyrgios has suffered a scare just five days out from the Australian Open, forced to retire in sweltering conditions at the Kooyong Classic on Wednesday.
Kyrgios, 20, won the opening set 7-6 (7-5) and trailed 3-2 in the second when he called time against Belgian world number 16 David Goffin as the temperature soared above 40 degrees Celsius in Melbourne.
The Australian world number 30, who requested a medial timeout in the first set, has been in good form in 2016.
He led Australia to their first Hopman Cup since 1999 following wins over Andy Murray and Alexandr Dolgopolov in Perth.
Kyrgios had struggled in the heat at Kooyong, with several verbal exchanges with the chair umpire over tight line calls.
He heads to the Australian Open looking to improve on his quarter-final appearance of last year.