Officials at the ATP Stuttgart event on Sunday issued an apology to Nick Kyrgios, who exploded on court a day earlier after being racially heckled during a semi-final loss to Andy Murray.

Kyrgios was verbally set upon by a small group of courtside spectators as he went down 7-6(5), 6-2 to his Scottish opponent.

Kyrgios exploded with a racquet smash and drew a point and then a game penalty early in the second set for unsportsmanlike conduct.

The 27-year-old said he was the target of racists and posted a complaint on Instagram.

“We have expressed our regret to Nick Kyrgios and his team at what has happened and have assured him that we do not accept such behavior,” a tournament statement read.

“The incident is currently being investigated by those responsible.”

“The ATP tournament in Stuttgart stands for creating an integrative environment for all players, coaches, visitors and employees in which discrimination – of any kind – has no place.”

It added; ‘This attitude is lived by those responsible and therefore has top priority for the event, as does compliance with sporting values such as fairness, tolerance and team spirit.”

“In this sense, no discriminatory statements on the part of viewers will be accepted.”

Kyrgios will play this coming week at the ATP 500 tournament in Halle, northern Germany.