The Ireland front row looked in discomfort after being replaced early on in the 27-15 defeat by Scarlets.
"Jack got a whack on his arm so we'll see how he is. He may need to get an X-ray," said Leinster coach Leo Cullen.
Sean O'Brien, another Lions squad member, was a late withdrawal from the Leinster bench because of a tight calf.
Flanker O'Brien hasn't played since missing Leinster's European Champions Cup semi-final defeat by Clermont on 23 April because of a hamstring problem.
His ongoing fitness issues are likely to be a concern for Lions coach Warren Gatland, with the squad departing for New Zealand on 29 May.
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Leinster prop Tadhg Furlong, also part of the Lions squad, hobbled off in the second half of Friday's defeat by Scarlets but his issue was said to be cramp.
Lions fly-half Johnny Sexton required treatment during the game but was unscathed afterwards.
Garry Ringrose, a possible contender for a late Lions call-up if any of the selected centres are ruled out, also appears to be fine despite coming off late in the game with a knee injury.
Wales hooker Ken Owens missed Friday's semi-final because of an ankle injury but Scarlets coach Wayne Pivac said on Saturday that the 30-year-old should be fit for the Lions tour.
Prop Jack McGrath is a fitness concern for the British and Irish Lions tour after injuring an arm during Leinster's Pro12 semi-final defeat.