Saints chief executive Mark Darbon says the club are expecting South African star Heinrich Brüssow to link up with the squad in mid-January.
Brüssow was signed to fill the void left by Louis Picamoles, who was sold to Montpellier at the end of last season.
But the new man has to complete his commitments with Japanese club Docomo Red Hurricanes before moving to Northampton.
Brüssow's arrival will be a big boost for Saints, who have lost 12 of their past 13 matches in all competitions.
The 31-year-old Springboks flanker, who has won 23 caps for his country, will bring a wealth of experience.
Darbon said: "He should be here by mid-January at the latest.
"It's just reaching the end of the season in Japan so we're just working through the exit timings.
"It will be by mid-January at the latest, but potentially before that."
Sam Dickinson had returned to Saints on a short-term contract as cover before Brüssow's arrival, but his contract reached its conclusion on December 31.
Dickinson is yet to finalise his next destination having made a total of 96 appearances during his two spells at Northampton.