Novak Djokovic was set to lead his country in the ATP Cup on Saturday, but the world No. 1 pulled out of the tournament earlier this week.
That responsibility now falls to Dusan Lajovic, but it's still unclear whether nine-time champion Djokovic will defend his title in next month's Australian Open.
It's been stated that all players must either be vaccinated against COVID-19 or secure a medical exemption from the Victorian Government, which Djokovic is yet to receive.
Djokovic has repeatedly refused to say whether or not he is vaccinated, but he has previously voiced vaccine scepticism and has spoken out strongly about his belief that athletes should have the right to choose.
Ahead of the ATP Cup, Lajovic commented on the absence of his Serbian team-mate, "Unfortunately he's not able to come here but he was I think hoping, same as we did, that somehow he will be here. Unfortunately he's not, and we've got to deal with it."
Regarding Djokovic's chances of playing in Melbourne, Lajovic added: "He just said that he's not coming to the ATP, and is trying to get to Australian Open."
If Djokovic is eventually given the green light, he has already missed out on some key preparation, with a number of stars already arriving in Sydney and training.
Time is ticking for an announcement to be made, with the tournament set to start on January 17.