Chairman Tony Hewitt says Saints are still hoping to sign two more players this summer.
The club have identified a lock and a centre as the primary targets ahead of next season.
Saints have already announced deals for France No.8 Louis Picamoles and South African scrum-half Nic Groom.
But they remain on the look-out for a man to fill departing second row forward Victor Matfield’s boots as well as a player to increase competition in the centres.
And Hewitt said: “We’re really looking for two more players.
“We want a second row because we’ve obviously got to replace Victor Matfield and we also need another top three quarter to enable us to rotate the squad a bit more.
“Those are the two main positions we’re concentrating on at the moment.
“With the French clubs and English clubs having more money, the process becomes slightly more complicated now in achieving what we want to do quickly.
“It takes a bit longer to do these signings, but we are in negotiations in both of those positions.”
Samu Manoa has been linked with a return to Saints, but the American star, who left Northampton for Toulon last summer, has three more years of his big-money deal remaining.
And Hewitt said: “Samu is under contract at Toulon so they would have to release him.
“We’re looking at every possibility to secure the right person for Northampton.”