Australian Open holder Djokovic, who went on an 18-0 run at the start of the season, confirmed there would be three big names apart from himself at the June 13-July 5 tournament.
“I am delighted that Dominic Thiem, Grigor Dimitrov and Alexander Zverev will be my guests here in my hometown,” said the 17-times major champion.
“This is the first time any of them will be playing here and I will do everything in my power to be a good host.
“We would dearly love for fans to be able to attend but that’s still not certain because we have to abide by the Serbian government’s coronavirus regulations.”
The first leg will take place on red clay in Belgrade on June 13 and 14 at Djokovic’s complex and the second in Croatia’s coastal resort Zadar on June 20 and 21.
Montenegro and Bosnia have been designated to host the final two legs but Djokovic said the infrastructure was still not in place.
“Bosnia and Montenegro are still not 100 per cent certain as the hosts of the final two legs because we haven’t had enough time to prepare the infrastructure, but we are very nearly there.
“As for the three big names coming over, they will all play in the opening leg in Belgrade. Zverev might play in Croatia too while Dimitrov could appear in Croatia and in Montenegro.”
All four tournaments will feature eight players, competing in two pools of four on a round-robin basis with the winners of each pool advancing to the final.
Djokovic added sets would be slashed to winning four games instead of six, with a total of 13 matches to be played over two days in each leg.
Asked whether he considered inviting longtime rivals Roger Federer and Rafael Nadal to the event, Djokovic said: “Quite frankly, inviting Federer didn’t cross my mind because … he is still nursing a knee injury.
“As for Nadal, I have no problem giving him a call but I wouldn’t expect him to come over.”