Conor O'Shea has warned that Harlequins' stunning Heineken Cup victory over Toulouse "counts for nothing" unless they back it up by beating Gloucester on Saturday.
Quins' success in France almost four weeks ago kept them on course for an automatic quarter-final place from Pool Six, leaving them just one point behind the French heavyweights, who host Connacht on Saturday and then travel to Gloucester next Friday, while Quins entertain Gloucester before visiting Connacht.
And rugby director O'Shea said: "The victory in Toulouse was a seminal moment for the club, but it counts for nothing if it is not backed up on Saturday. Gloucester represent a huge challenge to us, as they are developing one of the most talented squads in the country."
Cardiff Blues can take a grip on Pool Two if they beat London Irish at the Madejski Stadium on Saturday Edinburgh lose against Racing Metro in Paris on Friday night.
"Irish play a strong brand of rugby, a physical brand of rugby, and depend heavily on momentum being generated by their forwards," Blues backs coach Gareth Baber said.
Leicester captain Geordan Murphy, meanwhile, has predicted "an arm wrestle" when the Tigers fight to keep alive their Heineken Cup quarter-final hopes in Belfast on Friday.
Pool Four leaders Ulster stand two points above Leicester with just two group games left, while French heavyweights Clermont Auvergne also have realistic last-eight hopes, lying just a point behind Murphy's men in third.
If Ulster win at Ravenhill by more than seven points, then the Tigers are effectively looking at pool stage elimination for only a fifth time in 15 European campaigns, and full-back Murphy said: "We are going to have to put in a very good performance up front, be defensively sound to stop them scoring tries and kick our goals."
Winning is the only option for Welsh challengers the Ospreys when they host Pool Five opponents Treviso on Friday. The home side are currently six points adrift of group leaders Saracens, largely as a result of suffering back-to-back defeats against the reigning English champions last month.
Elsewhere, twice European champions Munster could secure qualification from Pool One if they beat Castres on Saturday, while Scarlets host Northampton in the same group, Pool Three strugglers Bath visit Montpellier and Clermont face Aironi in Monza.