Francois van Wyk says Saints will have an honest review after admitting they were simply not good enough against Saracens.
The black, green and gold were beaten 54-28 in Sunday's Premiership Rugby Cup clash at Franklin's Gardens, shipping seven tries in the process.
They had gone in only 23-21 down at the break but lost the second half 31-7 as their hopes of defending the trophy they won back in March faded away.
Saints will conclude their cup campaign on Saturday, at Leicester Tigers.
And South African loosehead prop van Wyk knows they need some rapid improvement to be ready for the Gallagher Premiership opener at Saracens on October 19.
"It's frustrating because we talk about it and we need to improve because the Premiership is round the corner," van Wyk said.
"We need to come back in, look at ourselves and just be completely honest and say 'it's not good enough'.
"Saracens are a good side and you can't fault them on that, but we just need to get better, especially in our exits and our one-on-one tackles - we can't slip off.
"It's frustrating because you want to win and that's why you play the game.
"I don't think we have to see it as a pre-season. It's about taking it game by game and we need to get that confidence from winning back.
"This weekend is going to be tough, away from home, and we know it's a derby game so we need to be on our A game."
Sunday's game gave van Wyk a chance to get his first minutes of the season.
He said: "I had a bit of a longer pre-season so I was in the gym for a bit longer than the other boys.
"I feel like it's benefitted me in a way so I'm pretty happy with that.
"I felt pretty good on Sunday but I can get better."