While Jamie Heaslip currently leads the nation, there is a strong body of opinion that O'Brien is a better option straight off the base of the scrum as a carrier.
The Tullow man does accelerate from 0-60 faster than your average 2-litre engine. He must be bursting to get out there and blast away at Glasgow. He is not the only one. Quinn Roux arrived from South Africa with a reputation as a man mountain who could move with aggression and speed.
An unusual injury to Roux's chest has hampered his involvement, which has been a frustration for the coaches who have liked the cut of his jib from the outset. The former Western Province second row has not played since the 13 minutes leading up to his injury against Connacht in September.
It will be interesting to see how Roux combines with Leo Cullen on the same day another lock signing Tom Denton starts for Leinster 'A' at the Sportsground.
The remarkably consistent Isa Nacewa returns from injury into the No 15 jersey. Ian Madigan moves into the controls at out-half.
In the pack, hooker Aaron Dundon also returns from the casualty ward for his first impact since his only other one against The Scarlets at the start of September.
The Warriors are flying high in third, five points ahead of Leinster, and they have been beaten just once at home by their visitors since 2007.
The Achilles heel for Glasgow could come at scrum-half where all four scrum-halfs are unavailable for one reason or another. Development nine Sean Kennedy will have to hold his own against an all-international back row of Kevin McLaughlin, Shane Jennings and the marauding O'Brien.
GLASGOW WARRIORS V LEINSTER, SCOTSTOUN, TONIGHT, 7.35
GLASGOW: P Murchie; T Seymour, A Dunbar, P Horne, DTH van der Merwe; R Jackson, S Kennedy; G Reid, P MacArthur, M Cusack, T Swinson, T Ryder, R Harley, C Fusaro (capt), J Strauss.
LEINSTER: I Nacewa; D Kearney, B Macken, A Goodman, F Carr; I Madigan, I Boss; J McGrath, A Dundon, J Hagan, L Cullen (capt), Q Roux, K McLaughlin, S Jennings, S O'Brien.
Leinster's young guns take aim at Sportsgrounds
Connacht v Leinster, The Sportsground, 5.0
The most interesting fact about this Leinster collective is that six of them, including captain Conor Gilsenan, played for Ireland in the U20 World Cup in June.
This is a measure of the youthful look to the side with full-back Adam Byrne and centre Rory O'Loughlin both under-age for this season's Ireland U-20s.
CONNACHT: M Jarvis; M McCrea, C Finn, B Murphy, S MacAuley; J Carty, P O'Donohoe; B Wilkinson, K O'Byrne, JP Cooney, U Dillane, J Gardiner, D Heffernan, E Grace (capt), A Conneely.
LEINSTER: A Byrne; A Boyle, R O'Loughlin, J Coghlan, M McFarland; C Marsh, L McGrath; J Treacy, B Byrne, T Furlong, T Beirne, T Denton, B Marshall, C Gilsenan (Capt), J Conan.