Jim Mallinder admits Exeter's physicality took its toll on Saints as they slumped to a 36-12 defeat at Sandy Park.
Mallinder's men conceded five tries in a loss that has left them three points behind sixth-placed Harlequins ahead of the final-day meeting between the teams at Franklin's Gardens next Saturday.
Saints did manage to score through JJ Hanrahan and Ahsee Tuala, but they were totally overwhelmed by rampant Exeter.
And Mallinder said: "The lads are all down because a lot of effort was put into that game.
"We've got a few knocks, plenty of tired bodies because we did defend with intent, but in the end it took its toll.
"A lot of credit to Exeter for being on the front foot and being so physical."
Saints now face a huge fixture against Quins at the Gardens next weekend as they bid to finish sixth and secure Champions Cup rugby for next season.
Mallinder's men must win by more than seven points as they currently trail Quins by three points and the side from The Stoop have won two more league matches this season.
And Mallinder said: "Next week is a massive game.
"We know (eighth-placed) Gloucester aren't fully out of it yet so we'll watch them (at Bath) with interest tomorrow.
"We need to regroup and put in a big performance next week."