Novak Djokovic was embroiled in a controversy during his quarter-final win over Japan’s Kei Nishikori at Wimbledon on Wednesday.

It all started after the Serb was given a code violation for ‘unsportsmanlike conduct’ after bouncing his racket on grass behind the baseline.

Djokovic was clearly unhappy as he went up to chair umpire Carlos Ramos and had a discussion with him.

His frustrations doubled up after Nishikori did the same in the fourth set but didn’t pick a violation, much to the dismay of Djokovic.

“Double standards, my friend, double standards,” Djokovic said before appearing to hit Ramos with a ball (see video below).

Addressing the issue in the post-match press conference, the 12-time Grand Slam champion said: “To be honest, I thought it was unnecessary to get a warning. I didn’t harm the grass. I knew how I threw the racquet.

“[Nishikori] even threw the racquet in the fourth set. He [Ramos] said he didn’t see it. It’s not fair, but it’s the way it is. In the midst of emotions in a tough match, it happens.”

This wasn’t the first instance of Djokovic losing his temper at the All England Club this year. During his third-round match against Britain’s Kyle Edmund last week, he had accused the crowd of being biased.

Djokovic will meet world No. 1 Rafael Nadal in the semi-finals on Friday.

Novak Djokovic @DjokerNole amaga con tirarle la bola al arbitro Carlos Ramos en su partido de cuartos de final de Wimbledon @Wimbledon #Djokovic #Wimbledon pic.twitter.com/dcuRviGKcU

— Tenis Málaga (@TenisMalaga) July 11, 2018