Stuttgart Open organisers are investigating a racism claim made by Nick Kyrgios after his straight sets defeat to Andy Murray on Saturday.
After losing the first set tie-break 7-5, Kyrgios smashed his racquet on the ground in frustration and received a point penalty.
In the second set Kyrgios conceded a game penalty for unsportsmanlike conduct as he continuously argued with the umpire before going on to lose the match 7-6(5) 6-2.
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Afterwards the Australian took to Instagram to explain that a racial slur affected his on-court behaviour and that the situation was "messed up".
He wrote: "When is this going to stop? Dealing with racial slurs from the crowd?
"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."
Tournament organisers said on Sunday they will investigate the incident.
"We stand for creating an inclusive environment for all," read a statement on the tournament's official website.
They added: "Discrimination of any kind is not tolerated.
"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."
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