Wales fly-half Sam Costelow has been ruled out of the Six Nations trip to face Ireland on Friday night.
Costelow, 25, suffered an ankle injury in the second half of the 26-23 defeat by Scotland nine days ago but was retained in the Wales squad last week.
The Scarlets number 10 is not fit to travel to Dublin but could still be involved in the tournament finale against Italy on 14 March in Cardiff.
Costelow is set to be replaced by either Jarrod Evans or Dan Edwards, who was dropped against Scotland after starting the previous seven matches.
Wales head coach Steve Tandy will officially name his team on Wednesday and will also have to replace injured flanker Taine Plumtree, who has been ruled out of the tournament with a shoulder issue.
Tandy has already added Cardiff prop Keiron Assiratti and Dragons flanker Ryan Woodman to the squad for the fourth game of this year's campaign.
Wales have lost 24 out of the past 26 internationals and are looking to halt a Six Nations run of 14 successive defeats that stretches back three years.
Wales have not beaten Ireland away in the Six Nations since 2012 or achieved a victory in Dublin since 2015.
- Agony and hope for Wales after Scotland loss
- 'Life in Welsh rugby' but stats show issues remain
- Six Nations fixtures, results, standings and how to follow on the BBC