It has been a frustrating few months for O'Connell and Munster and Ireland fans alike. He has not played since Munster's Heineken Cup round 2 victory over Edinburgh in mid-October.
The talismanic lock was subsequently involved in training with the Ireland squad for last month's GUINNESS Series, but he sat out all three games against South Africa, Fiji and Argentina.
The 33-year-old missed the summer tour to New Zealand earlier this year with a knee injury that kept him out for five months. He returned for Munster's Heineken Cup opener against Racing Metro 92.
The nature of the injury means he is a serious doubt for the final two pool games in the Heineken Cup next month and the start of Ireland's RBS 6 Nations campaign.
Meanwhile, O'Connell's former provincial colleague Tomas O'Leary is set to miss the rest of the season due to a back injury.
The Ireland scrum half, who joined London Irish from Munster earlier this year, is facing a 'four to six month lay-off'. He has not played for Irish since late October and has had surgery on a 'degenerative pre-existing injury' in his lower back.
In a statement on the 29-year-old Corkman, London Irish confirmed: "Tomas originally suffered an injury to his lower back in the Aviva Premiership match with Northampton Saints on October 6 and aggravated it during the first half of the match with Harlequins on October 28.
"Following further medical examination the decision was taken that surgery was necessary to solve this problem. He is not expected to be available for selection until April 2013 at the earliest."