The sight of John Millman practising with the Australian team has further fuelled speculation that rookie teenager Alex de Minaur may miss what looms as a crunch Davis Cup singles rubber against Germany in Brisbane today.
However, Australian team captain Lleyton Hewitt remains hopeful de Minaur will back up from his draining debut and contest the fifth, and possibly deciding, rubber of the first round tie at Pat Rafter Arena.
Australia must win both reverse singles rubbers to qualify for April's quarterfinals after Matthew Ebden and John Peers succumbed in five sets to Germany's Tim Puetz and Jan-Lennard Struff in a three hour doubles epic on Saturday, giving the visitors a 2-1 lead.
Australian number one Nick Kyrgios will first line up in his much anticipated clash with world number five Alex Zverev, a match Hewitt predicted would be a five-set thriller.
De Minaur, just 18, is then scheduled to face German number two Struff in what could be the tie decider.
However, there were doubts whether de Minaur would be able to back up after Millman, not the teenager, was seen hitting with world number 14 Kyrgios on Saturday.
World number 139 de Minaur was exhausted after finally succumbing in a five-set, almost four-hour loss to German star Zverev on Friday.
Hewitt said de Minaur would be given more time to prove his fitness.
"Hopefully he pulls up well," he said.
"We'll cross that bridge if we come to it. That's all stuff we will talk about after they get treatment."
German team captain Michael Kohlmann was surprised Kyrgios did not play doubles on Saturday but looked forward to seeing him line up against Zverev.
"That was the match everyone was hoping for, everybody was talking about. Now we will see," Kohlmann said.
"I think that Nick, if he's on and feeling it, he's tough to play for everybody, not only for Sascha (Zverev).
"But Sascha doesn't have the big pressure to deliver now we are 2-1.
"It might change just a bit in the mental game and the mental game right now in tennis is pretty huge."