In this year's RBS 6 Nations O'Driscoll broke Ian Smith's long-standing championship try-scoring record with his 25th try as Ireland denied England the Grand Slam, while he also scored a vital try in Leinster's Heineken Cup semi-final against Toulouse.
"Brian came off with a knee problem that was uncomfortable rather than unplayable. We'll have to see how it settles down over the weekend and then assess him, and the others, on Monday," said Leinster coach Joe Schmidt.
"It's not ideal because we want to have a good week of training ahead of the game against Saints.
"There were bodies littered all over the field at times. It was a really good, competitive match and it was superb preparation for the Heineken Cup final clash with Northampton."
Leinster dominated the first half leading 11-0 at the break thanks to a Fergus McFadden try and two Jonathan Sexton penalties.
Ruan Pienaar gave Ulster a foothold in the second half with a long-range penalty but it was all they could manage and a late Luke Fitzgerald try, converted by McFadden, finished things off for Leinster.
The Dublin side will now face either Munster or reigning champions Ospreys in the final in a fortnight's time.