Head coach Wayne Pivac will need assessments on four players ahead of next Saturday's Test.Â
Wing Josh Adams, who was due to line up at outside centre against Fiji on Sunday, was withdrawn just before kick-off due to a calf muscle issue.
Prop Tomas Francis had already pulled out after suffering concussion during training, while his fellow front-row forward WillGriff John and lock Will Rowlands suffered head knocks in Wales' 38-23 victory over Fiji.
Assistant coach Jonathan Humphreys said on Tuesday it is "unlikely" that Rowlands and John will be fit.
"They are following protocols, but I think it is unlikely they are going to be right," he said.
"Francis is again following protocols, so we are a bit more hopeful on that." Francis began the protocols on Friday.
On Adams, Humphreys added: "Hopefully, he is going to be right. It will probably be a last-minute clearance on that, but hopefully he is going to be right."
No.8 Aaron Wainwright has been recovering from a shoulder problem, and Humphreys said: "Again, it's going to be a late call.
"He has made significant improvement, so hopefully he will be involved at the weekend."
Wales went into the autumn series with star names such as Leigh Halfpenny, George North, Josh Navidi and Justin Tipuric all absent as they continued long-term injury recoveries.
And Pivac then saw several of his original squad - including captain Alun Wyn Jones and fellow British and Irish Lions like Ken Owens, Ross Moriarty and Taulupe Faletau - sidelined at various stages of the autumn schedule.
He added a number of players to the group, with hookers Bradley Roberts and Kirby Myhill making Test debuts, and he could again be forced to summon reinforcements as Wales prepare for the Wallabies.
Wales will tackle an Australian side beaten by Scotland and England during the autumn series, and having toppled the Wallabies twice in succession following a run of 13 successive defeats against them.
Pivac said: "Australia are well-coached - I know Dave Rennie very well.
"They have got a lot of quality throughout the side. They will be hurting after the last couple of games.
"We expect them to come and be physical. If the weather's good, it will be free-flowing, too, with any luck."
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