Ireland flanker Kevin McLaughlin will be out of the game for twelve weeks.
The blindside suffered a shoulder injury against Connacht which ultimately required surgery in what has been a depressingly inactive period in his career.
In recent times, McLaughlin has played lesser games every season from 26 in 2011-2012 to 20 in 2012-2013 down to 14 last season and just five this terms with the prospect of three months on the sidelines.
Leinster will be able to call on Ireland forwards Jack McGrath, Sean Cronin, Mike Ross, Devin Toner and Jamie Heaslip and full-back Rob Kearney to add quality to the return of centre Ben Te'o, now recovered from a fractured forearm.
Ulster coach Neil Doak will delay his decision on whether to include scrum-half Ruan Pienaar and/or number eight Roger Wilson until closer to the team announcement on Friday.
The return of Pienaar from a strained knee was pencilled in for the Connacht Interpro. That didn't come to pass.
Now, the South African playmaker will have to convince Doak that he is ready to resume his season in a real eight-pointer at The RDS.
The super-consistent Wilson led out the Northern Province on the occasion of his 300th appearance for the club against Connacht, a match in which he suffered a blow to his shoulder which makes him a doubt for Saturday.
The call on Academy hooker John Andrew to come in at flanker against Connacht last weekend is a reflection of how shallow the resources are there with Chris Henry and Nick Williams among those out injured.