Wales skipper Jac Morgan has suffered a dislocated shoulder and will miss the rest of the Autumn Nations Series campaign.
The British and Irish Lions flanker was injured in the act of scoring a try during Wales' 52-28 defeat to Argentina on Sunday, and watched the closing stages from the bench with his left arm in a sling.
Uncapped Ospreys back row Harri Deaves has been called up to replace Morgan for upcoming Test matches against Japan, New Zealand and South Africa over the next three weekends.
Wales head coach Steve Tandy said: "We’re all gutted to lose Jac – he’s a world-class player, as well as a great man off the pitch.
"But this gives an opportunity now for someone else and Harri has been performing strongly for the Ospreys for a consistent period."
Elsewhere, England are sweating on the fitness of Tommy Freeman (above) and Ollie Chessum after the British and Irish Lions duo emerged as doubts for Saturday's clash with New Zealand.
Both players sustained injuries in last weekend’s 38-18 victory over Fiji, forcing them to miss Monday’s practice session and placing uncertainty over their ability to train this week.
Freeman was replaced in the 67th minute of England’s ninth successive Test win because of a hamstring strain, resulting in Henry Arundell’s try-scoring cameo off the bench.
Chessum was also unable to finish the match due to a foot problem and the second row was seen using crutches at the squad’s Surrey base on Monday.
Head coach Steve Borthwick therefore faces the prospect of losing two certain starters for the visit of the All Blacks, who will be without the injured Caleb Clarke, to Twickenham Stadium in the main event of the autumn’s four fixtures.
If Freeman is ruled out, England can call on Tom Roebuck following his recovery from the ankle ligament damage that forced him to miss out against Fiji, with Arundell an option to provide bench cover once again.
Should Chessum fail to receive the green light, Maro Itoje and Alex Coles will form the second row with Chandler Cunningham-South the likely replacement lock.
England hope to name their team on Tuesday but the uncertainty over Freeman and Chessum, who were both Test starters on the Lions tour to Australia during the summer, means the announcement may be delayed until Thursday.
Meanwhile, Scotland stand-off Finn Russell (above) remains with the squad and will be assessed this week to determine whether he can be involved in Sunday's Test against Argentina at Murrayfield.
The 33-year-old was replaced in the closing stages of Saturday’s 25-17 defeat by New Zealand after problems with both his knee and his ankle, with head coach Gregor Townsend saying after the match "we hope he’ll be fit for next week".
There was no mention of Russell’s injury status in a squad update announced by Scottish Rugby on Tuesday morning.
It is understood that the talismanic fly-half is expected to train with the team as normal this week and will be assessed by medics as he goes.
Watch Ireland v Australia in the Quilter Nations Series on Saturday from 7pm on RTÉ2 and the RTÉ Player. Follow a live blog on the RTÉ News App and on rte.ie/sport. Listen to live commentary on RTÉ Radio 1
