The Greek player was denied his maiden major title by the Serbian player in the French Open final.
The world number four said that Novak Djokovic made vaccine players look like fools and that he was playing by his own rules.
The decision over whether the defending champion can stay in the country drags on, as top seed and nine-time winner Novak Djokovic remains in the Australian Open draw.
"For sure, he's been playing by his own rules and has been doing what not many players have the guts to do," said Greece's Tsitsipas.
The criteria for players to enter the country were announced by the ATP.
The visa of Novak Djokovic, who is unvaccinated, was revoked when he arrived in Australia last week, following questions over the vaccine exemption that would have allowed him to enter.
On Monday a judge overturned the decision and ordered his release from the immigration hotel after finding that border officials had not followed proper procedure.
On Wednesday, the Serbian tennis player admitted to meeting a L'Equipe journalist despite knowing he had tested positive for Covid, as well as making mistakes on his immigration forms.
Scott Morrison did not say when a decision about the Serbian tennis player might be made at the news conference.
It takes a lot of daring to do and put the Grand Slam at risk, which is why no-one really thought they could come to Australia unvaccinated and not have to follow the protocols.
I chose to go and be prepared for whatever was to come and not think about anything else.
97 of the top 100 male tennis players are vaccine free, according to the Association of Tennis Professionals.
American world number 93 Tennys Sandgren told reporters earlier this month that he had pulled out of the Australian Open because of the vaccine mandate and he didn't apply for a medical exemption.
"There are two ways to look at it," he said. One way is that almost every single player is vaccine free and did what they had to do in order to come and perform in Australia.
It seems that not everyone is playing by the rules, and that a small group of people chose to follow their own way, which makes the majority look like fools.
The Australian Open will be held in January. In the first round, the Serbian will play Ke cmanovic, while the Greek will play Ymer.