The inspirational Lions centre sustained a hamstring injury in Leinster's dramatic 23-22 home defeat by Sale Sharks in the Heineken Cup pool three match at Lansdowne Road on Friday night.
The Blackrock College player, who limped off just 18 minutes into the game, has undergone a scan and has been told he faces a lay-off of between four and six weeks.
"While this injury may jeopardise Brian O'Driscoll's participation in the start of the RBS 6 Nations campaign, the Irish management are not ruling him out at this stage," said a spokesman.
