Wales are set to be without locks Adam Beard and Cory Hill for their World Cup opener against Georgia on September 23.
Ospreys forward Beard had his appendix removed in Wales and did not travel to Japan with the World Cup squad.
And Hill is continuing his recovery from a stress fracture in his leg, remaining on target to be available for an appointment with Australia on September 29.
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“We’ve picked up a couple of injuries and there is a concern at the moment with the second rows,” said Wales head coach Warren Gatland.
“He [Beard] is hoping to come out to Japan on Thursday.
“He’s probably not going to be available for selection for the Georgia game, but we are hopeful – and the medics are confident – that he will be available for selection for the Australia game.”
It suggests that Jake Ball will be skipper Alun Wyn Jones’ second-row partner against Georgia, with flanker Aaron Shingler providing lock cover on the bench.
On Hill, Gatland added: “They [medics] are confident that he will be available for selection against Australia.
“He’s been out of his boot and on the training field today, even though he wasn’t doing any running.
“Hopefully, after that Georgia game he will be back training and available for selection.”
Fly-half Rhys Patchell, meanwhile, has done some non-contact work after suffering concussion during Wales’ final World Cup warm-up game against Ireland.
“He has gone through the HIA [head injury assessment] protocols,” said Gatland.
“He was training this morning, just doing some non-contact stuff at this stage.
“We will ease him back into contact work later in the week, making sure that we go through the protocols and ensure he’s 100 per cent and available for selection.”
The Wales squad are enjoying temperatures of around 30 degrees and unbroken sunshine in the southern Japanese city of Kitakyushu, where they will be based until Thursday.
They have also received a warm welcome, with hundreds of schoolchildren greeting their arrival at the airport while banners and flags of support are draped all over the city.
“It’s absolutely fantastic,” said Gatland. “They have embraced Wales, the team and the culture, even putting the red dragon on their fire engines.
“For the players to see all the flags and posters around town has been quite humbling. It’s brilliant that the city has got behind us.