Japanese spearhead Kei Nishikori admitted on Monday he was "very sore" as he resumes training after two weeks in hard lockdown, as their ATP Cup team frets on doubles specialist Ben McLachlan who is stuck in New Zealand.
Former top-five star Nishikori was among 72 players forced to stay in their rooms 24 hours a day after Covid-19 cases were detected on charter flights bringing them to Melbourne for the Australian Open.
Others were permitted five-hour daily blocks outside to train.
"It is obviously not easy. My body is reacting very tough," said Nishikori, who has slipped to 41 in the world after a series of injuries.
"Very sore everything. But I have still two more days, so I should be okay."
Japan open their ATP Cup campaign on Wednesday against Russia, with Nishikori facing world No 4 Daniil Medvedev and Yoshihito Nishioka up against eighth-ranked Andrey Rublev.
McLachlan, who has a New Zealand father and Japanese mother, is due to play doubles but is yet to arrive in Australia.
His plans were thrown into disarray when Australia halted its quarantine-free travel for New Zealanders last month after their first case of Covid-19 community transmission in more than two months.
The suspension has now been lifted and McLachlan is hoping to be on a flight on Tuesday.
"For a while Ben was telling us he had few options, that they were going to reschedule his route, itinerary," Japan team captain Max Mirnyi said.
"Only yesterday he confirmed they put him on a flight coming in tomorrow during the day."