English heavyweights Saracens and Leicester could secure European Champions Cup quarter-final places on Saturday if they maintain their unbeaten records in this season's competition.
Victory for Saracens against Allianz Park visitors Ulster would guarantee they finish top of Pool One prior to next week's trip to four-time European champions Toulouse.
Leicester, meanwhile, will progress as Pool Four winners if they beat Italian strugglers Treviso at Welford Road and principal rivals Stade Francais lose against Munster in Limerick.
With England's other four Champions Cup challengers - Wasps, Bath, Northampton and Exeter - also still in the quarter-final mix, it sets up an enthralling final two weekends of group stage action.
Saracens rugby director Mark McCall is confident his players will show an immediate response after suffering a first defeat of the season in 13 European and Premiership starts when Harlequins toppled the reigning league champions last Saturday.
"This group of players in the past has been pretty good at dealing with the odd setback," McCall said.
"We've got a big game to get our teeth stuck into against Ulster.
"They have players all over the field who are capable of winning games on both the domestic and international stage.
"In the past few seasons, Ulster have always been tough opponents for us, and they have made some real strides under Les Kiss in the last four or five weeks."
McCall fields seven of the eight Saracens players named earlier this week in Eddie Jones' England elite player squad, with full-back Alex Goode missing out because of a slight knock.
Centre Manu Tuilagi, who was also selected in Jones' squad ahead of the RBS 6 Nations Championship, makes his first start for 15 months after recovering from a serious groin injury when Leicester tackle Treviso, the only team in this season's top-flight European competition without a point.
Tuilagi returned to action as a second-half substitute when Leicester took on Northampton last weekend, but he now reclaims the number 12 shirt, partnering Mathew Tait in midfield. Tigers, though, are without fly-half Owen Williams (broken jaw) and flanker Brendon O'Connor (hamstring).
"We've worked hard to get into a position to contest the top spot in the pool, but the work is not finished yet," Leicester rugby director Richard Cockerill said.
"Treviso will make it tough - we know that from our own experience. We've met them regularly in the last few seasons, and they are always a hard team to play against."
Bath tackle Leinster in Dublin on Saturday, knowing that victory would keep alive their hopes of progressing from Pool Five, prior to hosting Toulon next weekend.
Bath head coach Mike Ford, who has retained the starting line-up on duty for last Sunday's 12-9 defeat in Toulon, said: "We have nine points and two matches left to play. We can still qualify, but we have to win our last two games."
And Exeter must beat Bordeaux-Begles away from home on Saturday to keep themselves on a quarter-final course from Pool Two, with Clermont Auvergne and the Ospreys also challenging strongly.
"We are in a very competitive pool," Exeter head coach Rob Baxter said.
"All we have to look at is what we can do, which is how we can go over there and play with great energy and in a way that wins us the game.
"We have to go over there with very little fear of losing, because losing is simply not an option for us. We have to go flat out for the win."
Exeter will be without the likes of injured trio Jack Nowell, Will Chudley and Geoff Parling, but Baxter added: "I believe we've picked a side that is fresh and energetic. It is still a very strong side.
"I don't want us to get caught up in history of past games or what is happening elsewhere in the pool, I just want to go over there and let a team off the leash and get a big performance from them."
In Sunday's Champions Cup action, Wasps, minus England forwards Joe Launchbury and James Haskell, visit Toulon, while runaway Pool Three leaders Racing 92 host the Scarlets and Northampton meet Glasgow in the same group, with Saints' England hooker Dylan Hartley back in action after being sidelined by a rib injury.