With Saracens and Leicester having already qualified for next month's knockout phase, Saints and Quins look set to join them.
Third-placed Quins will go through if they beat Worcester at Sixways, while a bonus point victory for Northampton against Franklin's Gardens visitors Sale Sharks means they would also progress. Gloucester remain in contention, but not only must they beat league leaders Saracens, they need other results to work for them.
"We obviously still need to get there, first and foremost, and that starts with winning against Sale," Northampton scrum-half Lee Dickson said. "But we have had a bad run of form in the play-offs in recent years and we have talked about that a lot. We had a chat in pre-season about it - we want to go that extra mile.
"It's knockout rugby from now on as far as I am concerned. Sale first and then Quins on the last day (of the regular season). Rugby is a strange game. You never know what can happen and any team can beat anyone. From third to seventh position only a few points have separated teams all season, which shows how tight it is."
Gloucester's play-off hopes suffered a severe blow when they slumped 32-9 against Sale last Friday, and prop Nick Wood said: "Some stern words have been spoken.
"The problem was that we were down early and everyone was trying to rectify it as individuals, whereas our strength this season has been grinding out wins by sticking together as a team. The hurt and the emotion will still be raw against Saracens, but that can be a good thing. It's a positive that we can get out there straight away and not dwell on it too much.
"It's frustrating because we really don't want to let one bad performance cost us in terms of what we have been aiming towards all season. That was the first match this season that we've not picked up any points and it came at just the wrong time."
Saracens are already guaranteed a home play-off and Leicester will emulate them if they secure three match points from their trip to Bath. Their opponents must win to keep alive a realistic chance of securing qualification for next season's Heineken Cup, while there is a key battle ahead on Sunday between two other top six contenders Wasps and Exeter.
In the other game, London Welsh visit London Irish knowing they are resigned to propping up the Premiership and left facing relegation following their defeat against Northampton last Sunday.