Jim Mallinder says Saturday's clash with Wasps is 'absolutely critical' for Saints.
Mallinder's men return to Aviva Premiership action on the back of successive Champions Cup defeats.
The most recent reverse came at Clermont Auvergne on Saturday as Saints failed to take their chances in a 24-7 loss.
It means they have now been beaten in each of their past three matches, with the European disappointments preceded by a Premiership defeat at Gloucester.
And Mallinder knows how vital it is for his third-placed side to get back on track at Franklin's Gardens this weekend.
"We've got to do that," the Saints boss said.
"We've lost last weekend's game and we've got to forget about Europe for a short period of time.
"This week becomes an absolutely critical game.
"We've got a home game against Wasps after a good start in the league, we're third, and we need to make sure we get a win to keep that momentum going."
Though Saints were beaten at Stade Marcel Michelin last Saturday, they could take plenty of positives from a game that they dominated for long spells.
And Mallinder, who had seen his side suffer a heavy defeat to Saracens six days earlier, said: "It was a completely different performance from the previous weekend.
"We were up against a tough side, away from home, in an atmosphere where were could have folded and we went down to 14 men (Dylan Hartley and Kieran Brookes were both yellow carded).
"It's disappointing that we conceded like we did but we had a fantastic comeback and though we only got one try on the board there were some fantastic pieces of play."