Flanker Justin Tipuric and scrum-half Rhys Webb are understood to be major doubts for Wales' autumn series opener against Australia on Saturday.
Tipuric has a thigh injury, while Webb is nursing a knee problem ahead of a demanding schedule that also sees Wales tackle Georgia, New Zealand and South Africa.
Wales are already without injured openside Sam Warburton -- the British & Irish Lions captain will not play again until later this season -- so 51 times-capped Tipuric's absence would prove a considerable blow.
Cardiff Blues' forward Josh Navidi, who has won three caps, could now make the back-row trio, potentially lining up alongside Aaron Shingler and Taulupe Faletau.
And if Ospreys number nine Webb is ruled out, then the Scarlets' Gareth Davies can expect a start as Wales look to end a run of 12 successive defeats against Australia.
"Justin Tipuric is carrying a bit of a knock, and so is Rhys Webb, so we will just wait until the last minute. The team is named on Thursday," Wales assistant coach and defence specialist Shaun Edwards told reporters.
"They will have to [take part in training] to put their hands up for selection. Both were on the Lions tour recently, and both played very well on that tour."
Wales head coach Warren Gatland, meanwhile, is expected to name Gloucester back Owen Williams at inside centre, with Scarlets wing Steff Evans taking over from an injured George North.
Edwards, meanwhile, is braced for a stern test against the Wallabies, who have arrived in Wales fresh from beating world champions New Zealand and then crushing 2019 World Cup host nation Japan.
"We all know what an unbelievable attacking threat Australia are, averaging 33 points a game," Edwards added. "If you look at our fixtures since Warren took over, they have always been tough in the autumn.
"We nearly always play the likes of Australia, South Africa and New Zealand, and we are playing all three this time. It is certainly not a resting month, put it that way.
"Australia are an immense attacking weapon. I would say they are the most potent attacking force in the first three phases in world rugby, probably even more than the All Blacks.
"They [Australia] are perennially a top-four ranked team, their attack is pretty prolific and they have a multitude of excellent backs."
Wales continued their autumn preparations by training against England's forwards in Bristol on Monday, with 2015 World Cup final referee Nigel Owens overseeing a session that concentrated on scrums and lineouts.
"It was good to go through our processes against England," Wales and Scarlets lock Jake Ball said. "We just wanted to make sure we got something out of it. I thought it was a good battle, and we got something out of it. We had some really good scrums and were happy with our lineout as well.
"When you train against each other week in, week out, everyone finds out what are your weaknesses, so it was nice to go up against an England pack you didn't know too much about. It's got added edge because it's against England. You want to put your right foot forward yourself as a player."