Dan Biggar is set to make his first Saints appearance when Chris Boyd's side travel to face Ospreys in Bridgend on Saturday (kick-off 3pm).
Biggar will be taking on the club he left during the summer as the teams square up in what will be Saints' first pre-season game of the summer.
The Wales fly-half is set to feature from the bench, along with fellow new recruits James Haskell, Will Davis, Matt Worley and Joe Gray, who signed on a three-month deal on Friday.
Prop Ben Franks, who moved to Saints after leaving London Irish this summer, does get a start, with new lock Dom Barrow also in the first 15 at Brewery Field.
There is no place in the Ospreys team for George North, who moved back to Wales from Saints during the summer.
The Ospreys clash will be the first of three pre-season matches for Saints with a trip to Dragons following six days later and a home game against Glasgow Warriors, on August 24, completing their preparations for the Gallagher Premiership opener at Gloucester on September 1.
Ospreys: Moss; T Williams, Thomas, Allen, Morgan; S Davies, T Habberfield; R Jones, Otten, Fia; Ashley, Beard; Volpi, S Cross, McCusker (c).
Replacements: Phillips, Jeffries, Botha, Nemsadze, Morris, Morgan-Williams, Price, Hook, Lake, Walsh, W Jones, Aubrey, Evans, K Williams, Dirksen, D Cross, John, Ratti.
Saints: Emery; Sleightholme, Dingwall, Hutchinson, Pisi; Grayson, Reinach; van Wyk, Fish, Franks; Barrow, Ribbans; Gibson, Brüssow, Eadie.
Replacements: Davis, Waller, Gray, Painter, Ratuniyarawa, Craig, Onojaife, Haskell, Ryan, Harrison, Ludlam, Mitchell, Tupai, Biggar, Collins, Burrell, Strachan, Worley, Tuitavake.