James Ryan will miss Leinster's final two games of Champions Cup qualifying after being ruled out for a month with an ankle strain.
The international lock, the latest from Leinster's sleek conveyor belt of young talent, will face a race against time in his hopes to impress Joe Schmidt and lay his claims to a Six Nations start against France in February.
Ryan was injured during his side's Thomond Park win against Munster on Boxing Day .
"It was a very unfortunate situation," said Leinster assistant coach Girvan Dempsey. "He went up to compete with Conor Murray in the lineout and then just came down awkwardly on his ankle or just caught the end of Jack Conan's boot and rolled it."
Meanwhile, former Munster coach and Leinster and Ireland assistant Alan Gaffney (70) has been appointed interim coach of Aviva Premiership strugglers Northampton Saints.
"I am really excited about the challenge ahead," said Gaffney. "Any coach would jump at the chance to work with the calibre of players Saints have. The squad have shown what they're capable of earlier in the season but they have not been able to perform at that level consistently."
Gaffney cut his teeth with the New South Wales Waratahs before moving to Ireland to work with Leinster as backs coach and then Munster.
Gaffney was backs coach under Declan Kidney as well as returning to Leinster.