The world No. 3 ranked tennis player Novak Djokovic was on Wednesday warned about spreading political messages at the French Open.

This follows Djokovic’s call to end the violence in Kosovo, he wrote “Kosovo is the heart of Serbia. Stop the violence” on a camera lens.

His action was in reference to recent tension in Kosovo, which declared independence from Serbia in 2008.

However, Serbia has never recognised Kosovo’s independence and there has been violence in the past days following the installation of ethnic Albanian mayors in the north of the country, with police and Nato troops clashing with Serb protesters.

French Sports minister Amelie Oudea-Castera said on France 2 that Djokovic’s message was “not appropriate” and that French Open director Amelie Mauresmo spoke with him and has been encouraged to insist on the principle of “neutrality” on the court.

Meanwhile, the International Tennis Federation said Djokovic’s statement did not violate any rules because the Grand Slam rulebook does not ban political statements.

However, Oudea-Castera said, “When you carry messages about defending human rights, messages that bring people together around universal values, a sportsperson is free to express them but in this case, it was a message that is very activist, that is very political.”

The minister says no one should get involved, especially in the current circumstances, and it should not happen again.

Djokovic has been warned.