Saints are out of the Anglo-Welsh Cup.
Jim Mallinder’s men had gone top of Pool 1 by beating Scarlets 50-10 at Franklin’s Gardens on Friday night.
And they would have progressed to the semi-finals had Saracens failed to beat Leicester Tigers at Allianz Park on Sunday.
But despite fighting back to 22-20 behind at one point, Tigers couldn’t get the job done.
Tom Croft’s late yellow card and a try from Sarries fly-half Tom Whiteley put an end to the Leicester challenge.
Saracens earned a 29-20 win and topped Pool 1, meaning they will now host Leicester in the semi-finals.
Pool 2 winners Exeter Chiefs are at home to Pool 3 winners Harlequins in the other final-four tie.
Saints will now have plenty of free time in March, with their Aviva Premiership game at Sale on Friday, March 3 followed by a two weekends without a game before Leicester come to Franklin’s Gardens for a league game on Saturday, March 25.