Novak Djokovic, who recently tested negative for coronavirus after testing positive during his Balkans charity event, told a Serbian newspaper on Wednesday that he still was not sure if he would play the US Open.

"I still do not know if I will play the US Open," the tennis world number one said in an interview with the Sportski Zurnal daily paper. "I will certainly not play Washington or Cincinnati as planned."

The ATP and WTA tours are set to resume next month, even though several professional players have contracted COVID-19. The US Open will be the first Grand Slam following the restart, due to get underway behind closed doors in New York on August 31.

Djokovic resumed training on Tuesday and said he would take part on clay events. "Participation at Roland Garros is certain for now, Madrid and Rome are part of my agenda," he said. The Serbian  said he thought the ATP's revised ranking system, due to be introduced in August, was "correct".

Djokovic said on July 2 that he and his wife Jelena had both tested negative for coronavirus after testing positive during the Adria Tour in late June. The couple had been self isolating since returning to Belgrade from Croatia, where the second leg of his ill-fated tournament was held.

Four players -- Djokovic, Grigor Dimitrov, Borna Coric and Viktor Troicki -- tested positive for the virus after the event which saw little social distancing and packed stands. Djokovic's coach Goran Ivanisevic also contracted COVID-19.

Players had embraced across the net, played basketball and even danced in a nightclub during the week of the first leg played in Belgrade. Djokovic, widely criticised for hosting the tournament, issued an apology, saying he was "so deeply sorry" that the event "caused harm". But Djokovic said the widespread criticism he received was like a "witch hunt".

"I see nothing but critics lately, many malicious. Obviously there is something more than criticism, as if there is an agenda, someone has to 'fall', a personality, a big name has to be the main culprit for everything," he said.