British men's number one Dan Evans says Novak Djokovic should "feel some responsibility" after Grigor Dimitrov, Borna Coric and Viktor Troicki all tested positive for Covid-19 after playing at his Adria Tour event.
Bulgaria's Dimitrov played Croatia's Coric on Saturday in the second leg of the world number one's event in Zadar, Croatia.
Andy Murray says it has been a "lesson for us all", while Nick Kyrgios says it was a "bone-headed decision" to play.
"I just think it's a poor example to set," said Evans.
Serbia's Djokovic is currently waiting to hear the results of his test, which was carried out earlier on Monday.
The world number one played against his fellow Serb Troicki - who is also his doubles partner - in the opening leg of the tour in Belgrade.
"Once you start having mass gatherings with people coming in from all sorts of countries, it's a recipe for it to kick off," Murray said, as he prepares for this week's Schroders Battle of the Brits.
"So it's kind of a lesson for all of us - if we weren't already - to take this extremely seriously, and to have as many safety measures in place as possible."
With Croatia easing lockdown measures before the event, players were not obliged to observe social distancing rules and were seen embracing at the net at the end of their matches.
Pictures on the tournament's social media site from Friday showed Dimitrov playing basketball with Djokovic, Alexander Zverev and Marin Cilic, while he also put his arm around Coric before their match.
Zverev, Cilic and Andrey Rublev, who also played, have tested negative, but suggested they will all now self-isolate for up to 14 days.
Troicki told Telegraf that his wife, who is pregnant, tested positive on Friday, before he returned a positive test on Sunday.
Evans, 30, thinks Djokovic - who is president of the ATP Player Council - has some questions to answer.
"Put it this way, I don't think you should be having a players' party and then dancing all over each other," Evans said.
"He should feel some responsibility in his event and how it's transpired."
The first leg of the tour in Serbia attracted 4,000 fans, and concluded with players dancing close together in a Belgrade nightclub.
"Running exhibitions is good," Evans continued. "But even if the guidelines in that country are not two metres, it's not a joke, is it?
"Even if the guidelines were taken away in this country to normal, I'd still be trying to keep myself out of the way as much as I could from other people.
"I just think there's been a total disregard to that, really, and it's very unfortunate Grigor has it, Coric has it. I hope there's no second guessing on the US Open now, because of some unfortunate events."
The US Open will be held without fans from 31 August to 13 September, despite some players voicing concerns about travelling to New York.
The Battle of the Brits will also take place behind closed doors in London from Tuesday. Jamie Murray, who is fronting the event, accepts he will now face even greater scrutiny.
"From our point of view, we're obviously doing everything we can to limit that from happening," he said.
"We know there will probably be a few more eyes on us after what happened to the Adria Tour, so everyone's got to be on top of their game when it comes to social distancing."
The organisers of the Adria Tour say Sunday's final in Zadar was cancelled "as a precaution and to protect the health of all participants and visitors".
A statement read: "At all times we have strictly followed the epidemiological measures in place with the countries where the Adria Tour was organised."
The ATP, the governing body of men's tennis, said it "continues to urge strict adherence to responsible social distancing and health and safety guidelines to contain the spread of the virus".
It added: "In planning for the resumption of the ATP Tour season from 14 August, ATP and other stakeholders have made exhaustive plans to mitigate risks through a variety of precautions and protocols to be implemented at ATP events."
There have been handshakes and hugs. They have got up close and personal to play football and basketball, and celebrated the end of the first leg in Belgrade with some improvised limbo dancing in a nightclub.
Crowds were made welcome by the authorities, but that does not mean social distancing should have been abandoned by the players, who had arrived from various different locations for the Adria Tour series.
And then onwards to others. Dominic Thiem, who was part of the show in Belgrade last week, has been playing in the Ultimate Tennis Showdown in the south of France this weekend.
Most of those on the Adria Tour have sounded distinctly lukewarm about the prospect of travelling to New York for the US Open - and it has not been hard to empathise with some of their concerns.
But when watching the pictures from Belgrade and now Zadar, the feeling is simply one of bemusement.
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