The 34-year-old Serb travelled to Australia after announcing he had received a medical exemption from Covid-19 vaccination rules to compete in the tournament.
That, however, was not sufficient for border officials with regard to entry into a country that has strict entry requirements. Djokovic was held for several hours at the airport after flying to Melbourne before ultimately being turned away.
Djokovic has challenged the Australian Border Force's decision to cancel his visa application and deport him and his appeal has been adjourned until 10am on Monday in Melbourne, court officials said.
Nadal, who caught Covid-19 last year, was asked about Djokovic's plight after his straight-sets victory against Ricardas Berankis at the Melbourne Summer Set tournament on Thursday.
He stopped short of encouraging his great rival to get vaccinated but added: "I have been vaccinated twice. If you do this, you don't have any problem to play here.
"The only clear thing is if you are vaccinated, you can play in the Australian Open and everywhere, and the world in my opinion has been suffering enough to not follow the rules.
"There are rules, and if you don't want to get the vaccine, then you can have some troubles. I think if he wanted, he would be playing here in Australia without a problem.
"He made his own decisions, and everybody is free to take their own decisions, but then there are some consequences.
"Of course I don't like the situation that is happening. In some way I feel sorry for him. But at the same time, he knew the conditions months ago, so he makes his own decision."