England and Northampton captain Dylan Hartley will miss Saints' Aviva Premiership clash against unbeaten Bath on Friday.
But Northampton say that Hartley, who has a hand injury, and flanker Tom Wood (shoulder) are "anticipated to be in training next week".
Hartley, who scored a try when Saints saw off Leicester last weekend, is replaced by Mikey Haywood, with Courtney Lawes leading the side.
Northampton, despite toppling Tigers and having a strong home record against Bath, face a tough task halting opponents that have beaten Leicester and Saracens this season.
Bath rugby director Todd Blackadder said: "I think it's an exciting challenge.
"They (Northampton) are a good team, and our challenge is to keep replicating the same performance.
"We need to go there and start really physical, and if we do that then the mind set will be right. We have got to turn up mentally."
Changes from the side that accounted for Saracens include starts for Bath's ex-Northampton scrum-half Kahn Fotuali'i and England international flanker Sam Underhill, who makes a first-team debut after joining from the Ospreys.