Lions tourist Rob Keraney has been dealt a big blow in the middle of the 2010 Six Nations.
The 2009 Lion is expected to be out of action for between three and five weeks after he picked up a knee injury last weekend.
Kearney will definitely be unavailable for Ireland's trip to Twickenham a week on Saturday and, although there is still a chance he could feature against Wales on March 13 or Scotland on March 20, it is feared he may miss the remainder of his country's Six Nations defence.
"Rob Kearney is rehabbing and is out for England," said Ireland coach Declan Kidney.
"We'd always give it 48 hours before confirming, but we expect him to be out for between three to five weeks."
If Kearney fails to recover before the end of the Six Nations, a possible return date could be Leinster's Magners League clash with Connacht at the RDS on March 27, with the Heineken Cup quarter-final against Clermont Auvergne taking place a week later.
The news comes as a huge disappointment to Kidney and the Ireland coaching staff who are looking for an immediate response to the comprehensive defeat to France in Paris in Round 2 of the tournament.
Kidney is now likely to turn to fellow Lions star Keith Earls to fill the full back role, with the Munster youngster having been used as a replacement and on the wing in the opening two games.