Stuttgart Open organisers are investigating the racism claim made by Nick Kyrgios on Saturday.
The Australian, 27, wrote on Instagram about alleged abuse aimed at him during his semi-final against Andy Murray.
Kyrgios, who lost in straight sets, was given a penalty after smashing his racquet and exchanging words with the crowd.
"We stand for creating an inclusive environment for all," organisers said in a statement.
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."
Kyrgios described the situation on court as "messed up".
"When is this going to stop? Dealing with racist slurs from the crowd?" he wrote on Instagram. "When I retaliate to the crowd I get penalised. This is messed up."
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