Best, O'Brien kept in cotton wool but Schmidt on tenterhooks as Six Nations stars go into battle
Ireland coach Joe Schmidt will be holding his breath this weekend as a number of his leading lights line out in Champions Cup action.
Although much of the action is meaningless, he will be hoping for a clean bill of health.
Some have taken the precaution of not starting at all. New Ireland captain Rory Best will miss the opportunity to lead his Ulster side in their tricky quest to become Ireland's only Champions Cup last-eight representative after a minor back issue ruled him out of contention.
Ulster's newest Six Nations squad member, centre Stuart McCloskey, is also rested for this afternoon's Belfast clash with Oyonnax (1.0), from which Ulster will hope that the bonus point-victory is accompanied by an unlikely pair of results in other pools.
"We're optimistic that we can get the job done and with the unpredictability of this competition, there's a real chance for us to go through," said director of rugby Les Kiss ahead of the only meaningful Champions Cup action involving an Irish province this weekend.
Leinster travel to face quarter-final chasing Wasps (3.15), seeking to avenge an opening-day humiliation but they have removed all six of the maiden European starters who produced thrilling displays in last weekend's defeat of Bath.
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Sean O'Brien and Mike McCarthy, despite both being fit, are not selected either in a squad that shows a massive 11 changes from last week.
Garry Ringrose, a cause celebre for Brian O'Driscoll and more this week after his omission from Schmidt's early Six Nations plans, is another not in the squad, having been given the early part of the week off.
Jonathan Sexton will captain the province for the first time in his career as he lines up against Jimmy Gopperth, the man who replaced him during much of his two-year stint in Racing Metro.
Another former Leinster player, Brendan Macken, features in midfield.
Munster's lack of depth is again evidenced by the fact that they make merely two changes to their side for the dead rubber away to Treviso at lunchtime tomorrow.
In the Challenge Cup, Connacht welcome back Ireland centre Robbie Henshaw after he recovered from a hand fracture as they seek the bonus-point win required in Galway (3.0).
Should they qualify, it is highly likely that they will have to travel for their quarter-final, with Grenoble, coached by their former hooker Bernard Jackman, their most probable opponents.