Wales and Cardiff number eight Taulupe Faletau is "touch and go" to be fit for the start of the Six Nations as he recovers from a knee injury sustained in training.
His Cardiff back-row team-mate James Botham is also a concern as he battles a neck problem.
Faletau, 34, was named in Warren Gatland's 34-man squad for the tournament after a 15-month absence from international rugby.
He will miss Cardiff's home European Challenge Cup game against Connacht on Friday night after being absent for the defeat against Perpignan in France last Saturday.
Wales open their Six Nations campaign against France in Paris on Friday, 31 January before travelling to face Italy in Rome eight days later.
Cardiff head coach Matt Sherratt says he is unsure whether Faletau will be available for the tournament opener.
"I'd imagine it'll be touch and go, but he may well get through," said Sherratt.
"He's not going to play this weekend. He's gone into Wales camp this week just to get physio and do some strength and conditioning.
"He basically felt a little bit of discomfort in his knee, a little bit of bruising. He'll be available sometime I'd imagine in the Six Nations. It's not anything to be hugely concerned about."
The British and Irish Lions number eight has made three Cardiff appearances this season in his latest return from long-term injuries.
Faletau started victories against Cheetahs and Dragons in December 2024 before coming on as a replacement in the New Year's Day draw against Ospreys.
He has not played international rugby since October 2023 and has missed Wales' entire 12-Test losing streak.
A broken arm in their final World Cup pool match against Georgia 15 months ago was followed by a broken shoulder on his return for Cardiff in April 2024 before his latest comeback.
So the injuries and complications with his recovery have limited the number eight to just three hours of rugby in the last 15 months.
Cardiff wing Adams is also unavailable this weekend, but is not currently considered a Six Nations injury concern.
The 29-year-old missed Wales' summer tour of Australia and three autumn defeats against Fiji, Australia and South Africa.
Adams has scored four tries in five games during his comeback from a knee injury which forced him out of action for six months but missed Cardiff's defeat in Perpignan.
"It is just a niggle," said Sherratt. "Josh has gone from quite a sustained period of inactivity and then he's come back and played five on the bounce.
"The Christmas period is busy and going from wet grass pitches to the Arms Park can take its toll a little bit. He can feel a little bit of discomfort in his groin.
"If we had to push him, we could play him this week. But we don't feel the need to do that and we need to look after Josh as much as possible."
Despite their injury concerns, Sherratt says he is delighted the pair are part of eight Cardiff players in the Wales squad.
"We are pleased for Josh and Taulupe," added Sherratt.
"The pair of them have worked so hard to get back from injury so them going back is a boost for us, them and a massive boost for Wales."
Wales trio Faletau, Adams and Botham are among 15 Cardiff players unavailable for the conclusion of the Challenge Cup pool stages this weekend.
Wing Theo Cabango is the most concerning after he was ruled out for the rest of the 2024-25 season with another hamstring injury.
Cabango has not played this season after damaging a hamstring against Ospreys in June 2024.
The other players unavailable this weekend are Tinus de Beer, Aled Davies, Corey Domachowski, Regan Grace, Mason Grady, Liam Belcher, Harri Millard, Iwan Stephens, Ben Donnell, Ed Byrne and Gwilym Bradley.