Cian Healy is facing a race against time to make Ireland’s Six Nations opener against Wales after undergoing a knee operation on Tuesday.
Leinster said the prop is expected to be out for three to four weeks after a scope and clear out of his right knee.
Healy hobbled out of the Pro12 win over Munster at Thomond Park on 27 December after coming off the bench.
The operation cleared out the joint, but the 28-year-old will now be sweating on his availability for the Aviva showdown on 7 February.
In better news for Leinster coach Leo Cullen, Luke McGrath has recovered from his foot infection and Johnny Sexton has trained fully this week, with both available for this Friday’s Pro12 trip to Ospreys.
Isaac Boss is continuing his recovery from a hamstring injury, while Mick Kearney has returned to non-contact on-field training as he steps up his comeback from a toe injury.
Jack Conan has had a protective boot removed as he makes progress from a broken foot.
Leinster haven't won at the Ospreys since 2009 and backs coach Girvan Dempsey is braced for another stern test.
"I think you look at them over the last five weeks they've been very impressive," he told leinsterrugby.ie.
"They've an international quality team. I think you look at them at the start of the season they were possibly similar to ourselves.
"They found it hard integrating those guys [who played at the World Cup] back in but they've shown that, if you look at their performances in Europe home and away to Bordeaux, they're still very much in Europe. They're fighting on two fronts over the next two weeks."
