Rory Best's ankle injury will be assessed over the next 48 hours but Dan Leavy's season appears to be over as it is feared that he suffered a leg fracture in a thrilling Champions Cup quarter-final between Leinster and Ulster.
Leinster prevailed 21-18 in a tight encounter and Ulster and Ireland skipper Best was an early casualty as he limped off in the 16th minute.
He returned later to watch the remainder of the game and was wearing a moon boot.
"With Rory, it's obviously an ankle and he is icing it now, we'll assess that over the next 48 hours," said Ulster boss Dan McFarland.
But Leavy, who only returned last week from a long-term calf injury after missing the Six Nations, looks set for another long absence.
"Dan has had a bad injury," said Leinster boss Leo Cullen.
"I don't want to get into too much detail. He will be out for a while. We will get it assessed and take it from there.
"It's a tough one for Dan."
Leinster expect to have Johnny Sexton and Robbie Henshaw back in time for the European semi-final clash with Racing 92 or Toulouse - the meet in the last eight tomorrow.
But following the loss for the remainder of the campaign of Josh van der Flier, the absence of Leavy now is a blow to the province's hopes of clinching back to back doubles in the Champions Cup and PRO14.
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