Leinster and Ireland flanker Rhys Ruddock has been ruled out for four to six weeks after suffering a broken arm.
Ruddock, 24, sustained the injury in Leinster's European Champions Cup win over Harlequins on Saturday.
The Leinster player started in Ireland's impressive autumn wins over South Africa and Australia.
Ruddock is now in danger of missing Leinster's two remaining European pool games next month and could also face a race to be fit for the Six Nations.
Dublin-born Ruddock was drafted into the Ireland team on the morning of the game against South Africa on 8 November after Chris Henry was taken ill.
Ruddock went on to score Ireland's first try in the win over the Springboks and held on to his starting role for the victory over Australia.
With Henry likely to be ruled out until the late spring after undergoing heart surgery and Sean O'Brien still out of action because of a shoulder injury, Ruddock's arm fracture will be a concern for Ireland coach Joe Schmidt.
Ireland begin their Six Nations campaign against Italy in Rome on 7 February.
Ruddock is a son of former Wales coach Mike Ruddock.
First up, Ruddock will miss Leinster's Pro12 game against Connacht on Friday and the Boxing Day contest against Munster.