Dominic Thiem played in the Belgrade leg of last month's ill-fated tournament organised by world number one Novak Djokovic.
Alexander Zverev and Nick Kyrgios were slated to join Dominic Thiem at an exhibition tournament from July 13-19 in Berlin.
The United States has seen an alarming resurgence of new coronavirus cases.
Dominic Thiem took part in the Belgrade leg of the exhibition event organised by Novak Djokovic, where matches were played in front of thousands of fans, earning a storm of criticism.
Alexander Zverev was heavily criticised after viral footage emerged of him partying in a busy bar despite pledging to "follow self-isolating guidelines" after playing in Novak Djokovic's coronavirus-hit Adria Tour.
Dominic Thiem took part in the Belgrade leg of the exhibition event organised by Novak Djokovic where social distancing was minimal and matches were played in front of thousands of fans.
Nick Kyrgios, Dominic Thiem and Alexander Zverev have been signed up to take part in Berlin.
Novak Djokovic appears doomed never to be held in the same saintly esteem as Roger Federer or Rafael Nadal, the undisputed 'people's champions' of tennis.
Novak Djokovic addressed 4,000 fans packed into the Novak Tennis Centre on the banks of the Danube in the first leg of his Balkans charity tennis tournament.
The US Open main draw is due to get underway in New York on August 31.
Top-level international tennis returns this weekend in Belgrade with a charity tournament hosted by world number one Novak Djokovic and where fans will be welcome.
The ATP and WTA tours are both suspended until late July due to the global health crisis.
Vijay Amritraj said the trio of Roger Federer, Novak Djokovic, and Rafael Nadal have a tight grip over Grand Slam tournaments and won't feel any financial stress or the pressure of progress.
Last month, Dominic Thiem had expressed scepticism about plans to set up a fund to help lower-ranked players struggling because of the shutdown of the sport.
Dominic Thiem said he would rather "give money to people or organisations that really need it".
Novak Djokovic is clear-sighted about his goals: overtaking Rafael Nadal's 19 Major titles and Roger Federer's 20 to become the all-time Grand Slam king, and outdoing the Swiss master's record 310 weeks in the top ranking.
Novak Djokovic defeated Dominic Thiem 6-4, 4-6, 2-6, 6-3, 6-4 to win record eighth 8th title at the Australian Open.
Australian Open final: Novak Djokovic is 6-4 in their career head-to-heads, but Dominic Thiem has won four of the last five.