The Ireland veteran escaped punishment at the time as referee Nigel Owens and his assistant didn't see the incident but he could face retrospective action from citing commissioner Eddie Walsh.
Kearney was knocked unconsciousness and was stretchered off immediately after O'Connell attempted to hack the ball on but instead made contact with his opponent's face.
The incident appeared more clumsy than malicious but that doesn't mean the 33-year-old cannot be punished for his indiscretion.
Any possible suspension would be a big blow for O'Connell who could miss the Heineken Cup semi-final against Clermont Auvergne next week.
O'Connell has only just returned from a lengthy lay-off due to a back injury but has already pressed his claims for a third successive Lions tour.
The 2005 and 2009 Test Lion was in superb form as Munster ended Harlequins' European dreams earlier this month and is even being tipped to follow Martin Johnson in leading the Lions on more than one tour.
A ban of any sorts could cast a serious shadow on those prospects, though, as head coach Warren Gatland is due to name his touring squad two weeks' tomorrow.
As for Kearney, the brother of Lions full back Rob seemed more concerned with whether he caught the high ball that immediately preceded his injury even though his season could well now be over.
"He was unconscious for a period of time. He's come back around and has probably asked the question 10 times, 'Did I catch it?'" said Leinster coach Joe Schmidt.
"He's going to be pretty relieved when he sees the footage that he did catch the ball. He's not in great shape at the moment. The main disappointment at the moment is, he has really come on.
"He's played a number of games in a row and was getting into a rhythm. He's likely to miss a few games now. That's probably his biggest frustration."