Just hours before his shock loss at the hands of Tommy Paul, Carlos Alcaraz's gesture for rival Alejandro Davidovich Fokina has gone viral.
Alcaraz was warming up in the gym before his clash with Paul when Fokina passed by him in the hallway outside.
With a smile on his face, Fokina knocked on the glass and held up his middle-finger to Alcaraz.
The 20-year-old laughed and mirrored his rival's gesture.
While it was all in good faith, it has not gone down well with several tennis fans.
One X (formerly Twitter) user said, 'When success goes to your head then this is what happens.'
As the incident happened on live television, one pointed out, 'When you forget you’re on live TV.'
A fan saw the lighter side of the exchange and commented, 'Yup, grand slam winner, still pretty much a teenager when he’s off the courts and goofing around with friends.'