Europe's elite tournament needs more uncertainty rather than another shakedown towards an inevitable Leinster-Toulouse final.
England lock Ollie Chessum will return to Leicester Tigers' starting XV on Sunday as his side host Saracens in the Gallagher Premiership.
Exeter picked up only their second Gallagher Premiership win of the season with a come-from-behind triumph against old adversaries Saracens.
Saracens player ratings: A dark day for former European heavyweights Saracens, who fell to an embarrassing 32-24 home defeat to an understrength Castres outfit.
Brad Barritt has full confidence that Maro Itoje is the right pick as captain for England, and potentially the British & Irish Lions.
Mark McCall’s Saracens were amongst the losers, but they at least could hold heads high in Limerick after an exhausting bonus-earning 12-17 loss at Munster.
The defeat shouldn't deny Saracens progress to the round of 16. Next weekend’s home game with Castres will likely herald a third win in four to guarantee their place in the knockouts but they will be hurt that they didn’t see this job through at Thomond Park.
There is no return for O’Mahony, whose last appearance came in the December 13 defeat at Castres.
Saracens director of rugby Mark McCall believes Tom Willis’ England debut is only a matter of time after the number eight spearheaded a 35-26 victory over Bristol at StoneX Stadium.