Connacht back Robbie Henshaw has withdrawn from Ireland's tour to Argentina with a hand ligament injury.
The 20-year-old sustained the injury earlier in the season but it had not limited his ability to train or play.
However, Henshaw exacerbated the injury in training this week and specialist advice recommended he has an operation to resolve the issue.
No decision on a potential replacement for the two-game tour has yet been taken.
Henshaw has been widely tipped to succeed the retired Brian O'Driscoll in Ireland's midfield, but will now miss out on the first chance to stake a claim for the vacant number 13 shirt.
Ulster's Darren Cave will now be favourite to start at outside centre for Ireland's Tests against Argentina.
Last week Paddy Jackson pulled out of the tour with a stress fracture in his lower back, while Dave Kearney is missing after injuring a knee.
The first Test in Resistencia, in the north-east of Argentina, will take place on Saturday 7 June.
The second Test will take place a week later in Tucuman, north-western Argentina, both with a 19:40 BST kick-off time.