The tennis world has been shocked by an act of disgusting behaviour that left Zhang Shuai visibly distressed on court.The Chinese player broke down in tears and retired from the match as a result of an incident during the first set against Amarissa Toth.Commentators around the world have been left horrified by the scene with saw Shuai robbed of a point - and the situation that followed exploded into a moment of immense controversy.

Zhang Shuai and Kiara Toth controversy

It began when Shuai sent a ground-stroke cross-court to Toth's right-hand side.

The ball appeared to land right on the line where the sideline meets the corner of the service box.

The Chinese native was stunned to see the ball was called out and argued with the chair umpire for several minutes.

She eventually called for a tournament supervisor to be brought on the court to address the matter.

Play continued for one more point, but disagreement over the call continued.

Video: The controversial point between Shuai & Toth

Shuai then spotted Toth walking to the area of the court where the ball landed and told her opponent not to cross out the mark with her shoes.

However, in a disgusting act of sportsmanship, Toth was seen on the TV cameras wiping the mark away with her shoes before officials could have another look at it.

Shuai was heard yelling: "Wait, wait, wait, keep the mark. What are you doing? Why would you do that?"

Toth responded: "Because you’re making problems, that's why."

Shuai was seen looking devastated at the change of ends following the service game, and a tournament doctor was eventually called onto the court.

The commentators noted that Shuai was shedding a 'flood of tears.'

Shuai got back on her feet and offered brief handshake with the chair umpire and Toth before making her way off court.

Toth held her hands in the air and celebrated immediately after the handshake.

What has Zhang Shuai said about the controversy?

Shuai addressed the situation on social media after the match, saying: "All efforts on practise was wrong.

"When you wanted to hit closer to the line, even touched the line still OUT.

"I love you guys and all girls who supporting me and standing by my side."

Toth has faced an avalanche of condemnation as a result of her on-court conduct.

Australian doubles star Ellen Perez was among the first to declare her disappointment, saying: "Well that's a quick way to lose respect from your peers.

"I'm actually shook by the level of disrespect from this girl.

"If I see this girl tomorrow I will tell her how disgusted I am."

It was a devastating episode for Shuai, who has previously opened up on her mental health issues.

She said last month she has been struggling to cope following the death of her grandparents this year.

She has also been dealing with personal issues with Chinese tennis officials that have resulted in her staying away from her country for the past three years.

Her opponent Toth, meanwhile, faces Ukrainian Kateryna Baindl in the round of 16 on Thursday. Something tells us she won't have too many neutral supporters.