Part of the reason O'Brien and co find themselves in this predicament is because when Exeter travelled to Dublin earlier in the competition, Leinster could only manage a dogged 9-6 victory.
And while O'Brien was the first to admit he was impressed by the Chiefs, he's adamant Leinster won't make the same mistake again.
"We can take it that they're a very physical bunch of lads," O'Brien told the Irish Independent,.
"To be honest, going into that game we didn't think they were like that, but we were soon woken up very quickly.
"Their work rate is outstanding and I think that that's what they pride themselves on. They're a very fit team, they have very strong set-pieces.
"They are just very good and they're very dangerous. We know all that about them now and we know how they can play when they have the ball.
"Their strength lay in the very agile back-row, first and foremost, with all three of them very smart. So, we're going to have to keep an eye on them.
"They caused us a bit of hassle that day in the ruck and in their counter-rucking. Causing a nuisance really, so we have to tighten up that area and, hopefully, it won't be a problem."
63x46.png){kind=logo}