The Aviva Premiership champions and current leaders need a point against Connacht at the Twickenham Stoop to guarantee they win Pool Three one game inside the distance. Quins have collected 19 points from a possible 20 in their European campaign so far, and Connacht are unlikely to halt their unbeaten run this weekend.
Saracens, meanwhile, will stay top of Pool One if they beat Racing Metro in Nantes. Defeat, though, and a final weekend shoot-out is likely between the Premiership club, Racing and Munster.
Heineken Cup newcomers Exeter face the toughest task of any team, tackling runaway Pool Five leaders Clermont Auvergne, who are unbeaten for 53 games at Stade Marcel Michelin.
"Clermont are very good at home and it will be a tough game as they are a top side, but we will give it a real go. We don't have anything to lose," Exeter wing Gonzalo Camacho said. "When we played them at Sandy Park (in October) we dominated the first half but didn't take our chances. We need to be better this time around."
Northampton face Heineken Cup elimination on Friday night unless they beat French challengers Castres at Franklin's Gardens. And the game's significance is not lost on Saints rugby director Jim Mallinder after Northampton gave themselves a Pool Four lifeline with victory over group favourites Ulster in Belfast last time out.
"We still have a massive point to prove in Europe, and the players know what is expected of them on Friday night," Mallinder said. "We need a win to keep our destiny in our own hands, especially as Castres are two points ahead of us in the pool."
Mallinder has made three changes from the side that accounted for Exeter last weekend, with wing James Wilson replacing Ken Pisi, look Samu Manoa taking over from Mark Sorenson and England flanker Tom Wood returning to back-row duty.
Ulster are also in action on Friday night, entertaining a Glasgow outfit that has collected just two points from four Heineken Cup games so far this season.
Gloucester, meanwhile, will be the first team through to this season's Amlin Challenge Cup quarter-finals if they defeat Bordeaux-Begles in France. Bath will also secure a quarter-final spot if they beat Agen at the Recreation Ground, when Worcester, Wasps and London Welsh are also in Challenge Cup action.