Fergus McFadden could miss all of Ireland's autumn Tests after being ruled out for six weeks by an ankle injury.
The wing, 28, was injured in Leinster's Pro12 defeat by Munster and the Irish province's coach Matt O'Connor said the injury was "pretty significant".
"It will tie him down for about six weeks," said the Leinster coach.
Ireland face South Africa in Dublin on 8 November before games against Georgia and Australia later in the month.
O'Connor added: "It looks like a pretty significant ankle strain but [there is] no surgery or other intervention which is really positive."
The Leinster back, who has won 28 caps, will miss the province's opening European Champions Cup games against Wasps and Castres on 19 and 26 October.
McFadden's ankle problem adds to Ireland's growing injury list which includes Lions flanker Sean O'Brien being ruled out for around five months by a shoulder problem.
|Ireland's autumn Tests|
|8 November: v South Africa - Aviva Stadium|
|16 November: v Georgia - Aviva Stadium|
|22 November: v Australia - Aviva Stadium|
Cian Healy is currently out of action because of hamstring problems while Ulster pair Iain Henderson (hip) and Dan Tuohy (broken forearm) are likely to be missing until the New Year.
Munster lock Donnacha Ryan is expected to be out for at least four months because of a toe problem which requires surgery.
McFadden's Leinster team-mate Luke Fitzgerald is also facing a race against time to return from long-term groin trouble for Ireland's November Tests.
Fitzgerald has not played since suffering groin trouble in March and O'Connor admitted the 27-year-old will still require a fortnight of reintegration once back to full fitness before he can return to action.
"How long is a piece of string?" added O'Connor.
"Jokes aside, Luke's progressing really well, he's putting in some positive strides. He's not very far away."