Cian Healy is a major doubt for Ireland's Six Nations opener after undergoing surgery on an ankle injury.
The Leinster prop missed last weekend's Heineken Cup win at Northampton and is expected to be sidelined for up to eight weeks.
Healy will miss Leinster's remaining Heineken Cup fixtures and Pro12 derbies against Connacht and Ulster, and faces a race against time to be fit for Ireland's opening Six Nations fixtures against Scotland on 3 February.
"Cian had ankle surgery on Wednesday so he's unavailable for about eight weeks," said Leinster coach Matt O'Connor.
Out of action
"It was syndesmosis and they repaired that. He's doing good but he won't play for a while."
The highly-rated Jack McGrath is likely to start at loosehead against Northampton Saints on Saturday while Michael Bent, whose preferred position is tighthead, will provide cover on the bench.
Meanwhile, O'Connor revealed that Sean O'Brien is likely to feature in the second half of Leinster's double-header with Northampton. The back-row is progressing well from a dead leg sustained in the first fixture at Franklin's Gardens.
"Seanie's trained all right so we'll wait and see," said O'Connor. "We'll give him as long as possible. It's improving really quickly but we'll just have to wait and see."