Ross out for six weeks and O'Brien back
Mike Ross will be right up against the clock to make it back for Ireland's Six Nations opener against Wales.
"He has got a high-grade hamstring strain and he is looking at somewhere around six weeks out.
It's a fairly significant injury," said Leinster team manager Guy Easterby (right).
"The protocols you follow in terms of those hamstrings is fairly consistent. I know that you've got your fast-twitch athletes and your other athletes."
There was no need to press home the point as to which category Ross resides in.
"At this point, there should be no particular issue. It is a significant high-grade hamstring strain, so he has to rehab that correctly."
Cian Healy's retrial from a botched hearing into his alleged strike against Guilhem Guirado's head will be heard on Wednesday.
The Ireland prop won't have to board an early flight to Paris for the hearing as it is scheduled to be carried out over Skype.
While Easterby was reticent when it came to discussing the incident for fear it would prejudice the proceedings, it is fair to say they are confident of a reversal of the guilty verdict.
Sean O'Brien has been cleared to return from that persistent imbalance born out of an inner ear impairment problem.
The openside just has to come through training this week to be on course for playing against Munster at Thomond Park on Sunday.
However, the form of Josh van der Flier could well tempt Leo Cullen to move O'Brien from seven or, indeed, to give the new sensation a week off.
Jonathan Sexton will have to wait until later this week to test out a minor quad strain, the same issue that hindered his World Cup.
Ian Madigan has shown all the patience in the world to wait his turn.
This could be his week as Leinster would not be inclined take a chance on Sexton.
Easterby was keen to point out the increasing importance of the PRO12 League, now that Leinster are out of Europe.
"From a Pro12 perspective, we're trying to grow the profile of the tournament," he said.
There will be no limit on Leinster's selection options for Munster due to the Player Welfare Programme.
"I think that's vitally important, certainly in terms of selection for the next couple of weeks."
The mere fact Leinster will not play in the Champions Cup quarter-finals will downgrade their profile when it comes to competing in the transfer market.
"Some people are more interested in money than others," said Easterby.
"Some people want to come and win stuff and you're weighing up all those things against the other clubs you're bidding with."