Andy Murray has encouraged Nick Kyrgios to maintain his professional standards after the Australian suffered another on-court lapse at the Shanghai Masters.
World number 14 Kyrgios appeared to give up late in his 6-3 6-1 loss to Germany qualifier Mischa Zverev on Wednesday.
He was involved in a verbal altercation with a spectator and was in a fiery mood during his post-match media conference.
Murray, speaking after his second-round win over Steve Johnson at the ATP 1000 event, spoke of the importance of players always giving their best.
"I didn't see the match. I've heard a little bit about it," the Briton, ranked second in the world, told Sky Sports.
"Nick will be disappointed, obviously, to have a performance like that. I know he likes his tennis, he knows a lot about the game.
"He had a great week last week and it isn't easy to back it up the following week if you're feeling a bit tired, a bit jaded, but you've got to give your best effort.
"That's your job - to give your best effort. If you're tired, or sick, you have to give your best on the day."