Nick Kyrgios was booed off court after he appeared to stop trying during a straight-set defeat by Mischa Zverev in round two of the Shanghai Masters.
The Australian, who said he was "bored" during his first-round victory over Sam Querrey, patted the ball over the net several times when serving.
He also began walking back to his chair before a serve from Zverev had landed.
The 21-year-old, ranked a career-high 12th in the world having won the Japan Open on Sunday, lost 6-3 6-1.
Kyrgios was last year fined $1,500 for a foul-mouthed outburst.