I don't see what else they could do. I mean, they might be able to let him stay in that quarantine/transit hotel, but he is for all intents and purposes "not in Australia." And it would not be happening IF he satisfied the border police with his reasons for medical exemption, but we don't know that either, correct? If they send him back to Serbia to get his visa, or wherever, this may be in part his fault, because now they really can't be seen as giving him preferential treatment, and the PM has already said that if his papers aren't in order, he's on the next plane, and no preferential treatment, etc. That tweet he made from the airport (in Marbella?) was ill-advised and incautious of the feelings of Australians, in retrospect, and he landed to find himself embroiled in a political mess that goes way beyond tennis now. Even the PM of Serbia has weighed in, and is using some sharp language.