Goran Ivanisevic, the coach of Novak Djokovic, tests positive for coronavirus

Ivanisevic, who said he has no symptoms, attended the Adria Tour exhibition series, a charity event hosted by Djokovic in Belgrade and at the Adriatic resort of Zadar in Croatia.

Four players from those events, including Djokovic and his wife, have said they have the virus. Grigor Dimitrov, Borna Coric and Viktor Troicki all said they also have it.

Thousands of spectators attended the matches in Belgrade and Zadar, and no social distancing was observed.

Dominic Thiem, who won the opening event in Belgrade on June 14, said Thursday that he has been tested five times but is negative.

The final for the event in Croatia was cancelled and subsequent matches in other countries were also called off.

Djokovic, a 17-time Grand Slam champion who has previously said he was against taking a vaccine for the virus even if it became mandatory to travel, said on Tuesday it was “too soon” to host such an event.

The coronavirus outbreak led to the suspension of the ATP and WTA professional tennis tours in March. Plans were announced last week for the sport’s sanctioned events to return in August.

But the infections have raised questions about the full-fledged return of competitive tennis, including the U.S. Open, which is scheduled to begin on August 31 without spectators. Djokovic has called the rules to keep everyone safe at the U.S. Open “extreme.”