Nick Kyrgios courted controversy again at the Shanghai Masters by retiring after losing the first set of his opening-round match against Steve Johnson.
The Australian was banned for showing a lack of effort and arguing with the umpire and fans during a second-round loss to Mischa Zverev at the same tournament 12 months ago.
Kyrgios did not appear injured and did not seek medical help before abruptly pulling the plug after Johnson claimed the first set 7-5 on a tie-break.
Both the American and umpire Fergus Murphy were bemused by Kyrgios' sudden retirement, which he later blamed on a stomach bug.
The 22-year-old cut a distracted and grumpy figure throughout and complained about Murphy several times.
When he was given a point penalty during the tie-break for an audible obscenity, having previously received a warning for angrily smashing two balls out of court, Kyrgios was heard saying he would quit if he lost the tie-break.
Explaining his decision, which drew boos from the crowd, Kyrgios wrote on Twitter: "I've been battling a stomach bug for the last 24 hours and I tried to be ready but I was really struggling on the court today, which I think was pretty evident from the first point."
Seventh seed Pablo Carreno Busta was beaten in the second round 7-5 7-5 by fellow Spaniard Albert Ramos-Vinolas while 15th seed Lucas Pouille fell 7-6 (9/7) 6-3 to Fabio Fognini.
Fourth seed Marin Cilic reached round three with a 6-3 7-6 (7/5) victory over Kyle Edmund and was joined by Juan Martin del Potro and US Open finalist Kevin Anderson.
John Isner saved a match point in beating Dusan Lajovic but Denis Shapovalov's first match as a top-50 player did not go to plan, the Canadian teenager losing 6-7 (3/7) 6-3 6-0 to Viktor Troicki.
Roger Federer's first opponent will be Argentinian Diego Schwartzman, who was a 6-4 7-6 (7/4) winner over qualifier Jordan Thompson.