MELBOURNE: Rafa Nadal said he feels sorry for Novak Djokovic after the world number one was denied entry into Australia but added that the Serb knew for months he could potentially face problems if he arrived without being vaccinated against COVID-19.

Djokovic, 34, was detained by officials at the border on Thursday amid a storm of protest about the decision to grant him a medical exemption from vaccination requirements to play in the Australian Open.

The player, who has won nine Australian Open titles including the last three, is holed up in a quarantine hotel in Melbourne as his lawyers sought an urgent injunction against deportation.

"Of course I don't like the situation that is happening," Nadal told reporters after winning his match at the Melbourne Summer Set ATP 250 tournament. "In some way I feel sorry for him.

"But at the same time, he knew the conditions since a lot of months ago, so he makes his own decision."

The 35-year-old Nadal tested positive for COVID-19 last month after playing at an exhibition in Abu Dhabi. The Spaniard said he faced "very challenging" few days.

Djokovic, who has publicly criticised mandatory vaccines, has refused to disclose his inoculation status and said he has been granted a medical exemption to compete in Australia.

Nadal said what has been happening was not good for anyone.

"Seems some rough situation," Nadal said. "It's normal that the people here in Australia get very frustrated with the case because they have been going through a lot of very hard lockdowns, and a lot of people were not able to come back home.

"I believe in what the people who knows about medicine say, and if the people say that we need to get vaccinated, we need to get the vaccine. That's my point of view."