Organisers of the Stuttgart Open have announced they're investigating Nick Kyrgios' claims of racial abuse during his loss to Andy Murray in the semi-finals on Saturday.
The Aussie star had to be persuaded to continue his match at the grass-court event after rowing with fans in the crowd.
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Kyrgios was embroiled in arguments and controversy, both with the crowd and the chair umpire, in a second-set meltdown before losing 7-6 (7-5) 6-2 against the rejuvenated former World No.1.
While fans were quick to condemn Kyrgios, he later revealed that he'd been racially abused.
"When is this going to stop? Dealing with racial slurs from the crowd?" he wrote on Instagram.
"I understand that my behaviour isn't the best all the time - but 'you little black sheep', 'shut up and play' - little comments like this are not acceptable.
"When I retaliate to the crowd, I get penalised. This is messed up."
On Sunday, organisers announced that they've launched an investigation into the matter.
"We stand for creating an inclusive environment for all players, staff members and visitors where discrimination of any kind is not tolerated. This attitude is lived by all people involved and responsible," tournament organisers said in a statement.
"These fundamental values are as important as values like fairness, tolerance and team spirit to us. Thus no discriminating actions by the spectators are accepted.
"We have expressed our regret towards Nick Kyrgios and his team and assured that any kind of discrimination is unacceptable. The incident is currently under investigation."
A frustrated Kyrgios got a code violation early in the first set tiebreak and then copped a point penalty after losing the set on what seemed a bad bounce on the final point.
Still raging as the second set kicked off, he was broken straight away after throwing in a couple of double faults, and amid arguments with the umpire and the crowd, was then docked a one-game penalty.
Evidently rattled by the comment from the crowd, Kyrgios refused to keep playing, sitting in his chair until the supervisor emerged to convince him to play on.
Having lost his focus completely, the Australian then delivered a number of errors as Murray sealed his spot in the final.
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Murray admitted after the match that it "wasn't fun in the end" as he reflected on the latest controversy involving Kyrgios, a friend he still believes has the talent to be one of the world's best players.
"You're always kind of battling yourself as well as the opponent, it's one of the difficult things about individual sports," said Murray, after reaching the 70th final of his distinguished career.
"Nick has the potential to be one of the best players in the world, there's absolutely no question about that. But, yeah, he obviously got very frustrated in the second set and made it a lot easier for me.
"It wasn't fun in the end. The second set wasn't a proper match. The end of the first set was deciding."
Later on Sunday, Matteo Berrettini won the Stuttgart Open for a second time after he beat Murray in the final 6-4 5-7 6-3.
Berrettini's triumph denied Murray what would have been his first title on grass in six years.
The Italian, who missed the clay-court swing after undergoing surgery on his hand in March, was playing in his first tournament since Indian Wells and triumphed on Sunday after Murray had injury issues of his own in the decider.
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