World No 1 Novak Djokovic has found himself under attack on multiple fronts after four more cases of Covid-19 emerged at his ill-conceived Adria Tour event, involving two coaches and two more players.

Nick Kyrgios, Andy Murray and Dan Evans were among the notable players expressing their alarm at the lack of social distancing in the Balkans, where Croatian No 1 Borna Coric and Djokovic's childhood friend Viktor Troicki joined Bulgaria's Grigor Dimitrov on the infected list.

The other two men who tested positive are believed to be Dimitrov's coach, Kristijan Groh, and Djokovic's fitness trainer, Marko Paniki.

But Djokovic himself refused even to take a Covid test on Sunday night in Zadar - the Croatian city where the final of the Adria Tour should have been held. Instead, he returned to Belgrade, where he and the rest of his family are understood to have been tested around noon on Monday. The results are expected to be released on Tuesday.

According to one Croatian report - which was described as accurate by Djokovic's management - he "decided not to be tested on the spot, because he does not feel any symptoms, nor anyone from his environment, including the professional staff".

The whole situation was criticised on Monday morning by Nick Kyrgios. "Boneheaded decision to go ahead with the 'exhibition'," said the Australian on Twitter. "Speedy recovery fellas, but that's what happens when you disregard all protocols. This IS NOT A JOKE."

Evans, the British No 1, took a similar position in a Zoom interview. "I just think it is a poor example to set," said Evans. "Even if the guidelines were taken away in this country I would still be trying to keep myself out of the way as much as I could from other people. And I just think there has been a total disregard to that."

During the two weeks of the Adria Tour, players have hugged and high-fived with abandon, and broken up the time between their matches by playing contact sports such as football or basketball. The Belgrade leg of the event concluded with them dancing shirtless in a nightclub, while photographs emerged of Djokovic and Dimitrov surrounded by a crowded pack of ball-kids. It is not only players and coaches whose safety has been compromised.

Evans suggested that these four infections were the predictable result of overly-casual guidelines. "It is very unfortunate that Grigor has it, Coric has it," he said. "But if you strip it back, is it a surprise? I think that is the question we should all ask. I hope there is no second-guessing now on the US Open because of unfortunate events."

Here is the main fear for many less affluent players whose income has evaporated during lockdown: that the Adria Tour scandal could threaten the resumption of the main tour. Thus far, there have been numerous other exhibition tournaments around the world, with no confirmed cases of Covid-19. But events in the Balkans are a reminder that young athletes in their 20s are not always content to self-isolate in their hotel rooms and read Proust.

"I have always had a good relationship with Novak," said Murray. "But what's happened is not a good look. When you are going through a time like this, it's important any of the top athletes around the world should be showing that we are taking this extremely seriously and knowing that we are using social-distancing measures and whatever it is.

"I hope that we learn from it," added Murray, "because ultimately the tour won't get back again if we are having problems every single week and the players are doing what they want. We need to make sure we are doing the right thing."

Djokovic was asked about the Adria Tour's lackadaisical approach to safety protocols 10 days ago, and replied that the event was simply taking its cue from government advice. Yet all the photographs of players dancing and horsing around had attracted widespread criticism even before Dimitrov became the first player to reveal his positive test on Sunday night.

On Monday, Noah Rubin, the American player who has become an unofficial spokesperson for lower-ranked players, described the outbreak as, "Just not okay. [It is] reckless and disappointing that they thought tennis deserved the risk".

This latest error of judgement comes on the back of several other PR mis-steps for Djokovic, who is also the president of the ATP Player Council. Since the beginning of lockdown, he has outed himself as an anti-vaxxer and questioned the restricted-entourage policy for the upcoming US Open. In early May, he posted a video of a practice session in Spain that broke lockdown protocols.

Numerous other players - including Danielle Collins, Sachia Vickery and Mitchell Krueger - have made critical comments about Djokovic on social media, whether because of the Adria Tour or his scepticism towards the US Open. Asked whether Djokovic should consider his position as president of the ATP player council, Evans stopped short of answering "yes" - but only just.

"I don't know," he said. "Put it this way, I don't think you should be having a players' party and dancing all over each other. When two very good tennis players have tested positive, you should feel some responsibility in his event and how it has transpired."

One of the 10 player representatives on the ATP player council - Jamie Murray's former doubles partner Bruno Soares - highlighted the damage that this episode could cause to Djokovic's political aspirations. During a podcast interview, Soares described the Adria Tour as a "horror show" and added: "It is embarrassing for him because he is the president and his speech goes against everything he showed in that event."

One of the other leading players involved in the Adria Tour - Dominic Thiem - has since moved on to play in the UTS exhibition event near Nice, sparking fears that he could be an asymptomatic super-spreader.

Meanwhile, Marin Cilic, Andrey Rublev and Alexander Zverev said that they would enter a 14-day period of self-isolation, despite testing negative. In a statement, Zverev said: "I deeply apologise to anyone that I have potentially put at risk by playing this tour."