Nicolas Kiefer questions the intelligence of Dominic Thiem & Alexander Zverev

Dominic Thiem's playing activity has come into question over the last few days, in the wake of the Adria Tour controversy. The ill-fated event hosted by Novak Djokovic came to a grinding halt in Zadar, Croatia after Bulgarian player Grigor Dimitrov tested positive for COVID-19.

The issue was exacerbated after it was revealed on Tuesday that three other players - Borna Coric, Viktor Troicki and Djokovic himself - had also contracted the virus

Dominic Thiem, who picked up the trophy during the first leg of the Adria Tour in Belgrade, was absent in Zadar due to his commitment to the Ultimate Tennis Showdown in Marseille. The Austrian got tested after his arrival there and was found to be negative, but his non-stop travel has attracted criticism from many fans and experts.

Now there's another critic on the scene, in the shape of former World No. 4 Nicolas Kiefer. The German slammed the players who participated in the Adria Tour, including Dominic Thiem and Alexander Zverev, for not following social distancing norms and disregarding public health and safety precautions.

The actions of Dominic Thiem, Alexander Zverev and others will have serious consequences: Kiefer

(From L to R) Alexander Zverev, Novak Djokovic, Grigor Dimitrov and Dominic Thiem

As per a report by German website t-online, Kiefer ripped into the organisers of the Adria Tour as well as the participants, calling the entire event a 'big mistake'. Kiefer also highlighted the errors in judgment by both Dominic Thiem and Alexander Zverev when they agreed to participate in the tournament.

"Alexander Zverev and Dominic Thiem are well-advised," Kiefer said. "Why does nobody tell them in advance: 'It's a nice invitation, but you shouldn't go'? You really have to wonder if they have anything in mind other than tennis balls."

Kiefer further highlighted how the Adria Tour debacle has jeopardized the French Open too. The German questioned the wisdom of playing the claycourt Major in front of spectators, as currently planned by the tournament director.

"This will have serious consequences," Kiefer said. "The French Open must actually be played in front of spectators. Will the risk not be too high after these events?"

All eyes will now be on Dominic Thiem as he goes through his packed schedule ahead of the restart of the season. He will first complete the Austrian Pro Series before going back to Marseille to rejoin the innovative Ultimate Tennis Showdown. Theim will then host his own invitational event called 'Thiem's 7' in Kitzbuhel, before finally playing an exhibition on grass in Berlin.

Dominic Thiem has also revealed that he will play the US Open and the Cincinnati Masters, meaning that he will pretty much be playing non-stop over the next couple of months.

The Austrian had put out a statement on his Instagram handle yesterday, apologizing for his mistakes during the Adria Tour. However, by refusing to take a breather and self-isolate for a couple of weeks - as recommended by experts, despite his negative tests - Thiem is opening himself up to the possibility of even more criticism.