Andrew Kellaway is set to make his Saints debut on Saturday - but two flankers have been ruled out of the game at Bath (kick-off 3pm).
Heinrich Brüssow (concussion) and James Haskell (ankle) will play no part at The Rec, with Jamie Gibson and Lewis Ludlam coming into the starting 15.
Mitch Eadie provides back row cover on the bench, with Tom Wood, who has been battling a groin problem, set to play for the Wanderers against Wasps on Monday night.
Kellaway recent strutted his stuff for the Saints second team, scoring in a win at Sale Jets.
And the Australian, a summer recruit from the Waratahs, will cover the 13, 14 and 15 positions from the bench.
"Andrew did pretty well for the Wanderers," said Saints boss Chris Boyd.
"His lungs were screaming at him towards the end of the game because that was the first game he'd played for quite a while.
"But he looked impressive with and without the ball.
"I think he can genuinely play 13, 14 and 15 so he's a good man to have in your 23."
Andrew Symons will make his first Saints start this weekend, lining up at outside centre, with Luther Burrell left out of the matchday squad.
Ben Franks is back in the No.3 shirt, replacing Ehren Painter, who is among the replacements.
Meanwhile, Dave Attwood, Taulupe Faletau, Aled Brew and Darren Atkins come into the Bath starting line-up for the Gallagher Premiership game.
Bath: Atkins; Rokoduguni, Brew, Willison, Cokanasiga; Burns, Green; Catt, Dunn, Thomas; Attwood, Charteris (c); Ellis, Underhill, Faletau.
Replacements: Walker, van Rooyen, Perenise, Stooke, Mercer, Cook, Priestland, Wright.
Saints: Tuala; Naiyaravoro, Symons, Francis, Collins; Biggar, Reinach; Waller (cc), Hartley (cc), Franks; Ribbans, Lawes; Gibson, Ludlam, Harrison.
Replacements: Haywood, van Wyk, Painter, Ratuniyarawa, Eadie, Mitchell, Kellaway, Mallinder.