The centre cum wing has been ruled out of Ireland's final autumn Test against New Zealand at the Aviva Stadium on Saturday and is expected to miss the back-to-back clashes with the English outfit on Saturday, December 7 at 14.
"Fergus McFadden has unfortunately fractured the fifth metacarpal in his right hand. He'll be sidelined for a number of weeks," said Ireland team manager Mick Kearney.
The first clash with Northampton is now less than three weeks away, meaning a more realistic European target may be the Round Five tie at Castres Olympique on the weekend of January 10/11/12.
McFadden has started both his side's Heineken Cup fixtures so far this term as the former champions won 19-9 at the Ospreys and 19-7 at home to Castres in October. That took his tally of European appearances to 29 since his debut in the 2009/10 campaign, with 26 coming in the continent's top-tier tournament and a further three in last season's Amlin Challenge Cup.
A Heineken Cup winner in both 2011 and 2012 and an Amlin Challenge Cup victor in May of this year, McFadden has just passed a century of appearances for his province in all competitions and now has 21 international caps for Ireland to his name having started both Tests since Joe Schmidt took over from Declan Kidney this term.
There could be further bad news for Leinster in the shape of Rob Kearney's rib injury, with the star full back unable to train at the moment. Ireland remain hopeful that Kearney will still be fit to feature against New Zealand on Sunday but it would be no surprise if he was instead forced into a period of recovery given the uncertainty surrounding his setback.
"Rob Kearney suffered a blow to the ribs and has a subluxed costal cartilage. This was very painful at the time and is improving well but he won't train for the early part of the week. It is very much a day-to-day injury and is hard to tell at this stage whether he will be available to play Sunday," continued the Ireland team manager.
Fellow Leinster back Brian O'Driscoll is also struggling with an injury picked up in Saturday's international defeat but the 34-year-old is hopeful of recovering from his calf problem in time to face the All Blacks.