Heinrich Brüssow will make his first Saints start when they square up to struggling London Irish at Franklin's Gardens on Saturday (kick-off 3pm).
The South African flanker came off the bench to make his debut in the Anglo-Welsh Cup win against Harlequins on February 2.
And he will now be in from the off as he lines up in the seven shirt in this weekend's Aviva Premiership encounter.
Luther Burrell returns from injury and starts at inside centre, making his first appearance since suffering a calf injury in the win against Gloucester on January 6.
George North has been released by Wales and will wear the 14 shirt, while Nic Groom replaces Cobus Reinach at scrum-half.
Alex Waller (arm) and James Craig (knee) are the only players currently sidelined by injury, while Dylan Hartley, Courtney Lawes and Harry Mallinder are away with England.
Meanwhile, London Irish name former Saints back Greig Tonks at fly-half for this weekend's game.
Experienced hooker David Paice will break Irish's all-time appearance record as he gets his 283rd game for the club.
Irish have won just once in the league this season, beating Harlequins at Twickenham on the opening day.
Saints: Tuala; North, Horne, Burrell, Foden; Francis, Groom; Ma'afu, Haywood, Brookes; Ratuniyarawa, Day (c); Gibson, Brüssow, Harrison.
Replacements: Marshall, van Wyk, Ford-Robinson, Ribbans, Wood, Reinach, Myler, Tuitavake.
London Irish: Marshall; Cokanasiga, Fowlie, McLean, Lewington; Tonks, van Zyl; Franks, Paice, Hoskins; van der Merwe (c), Paulo; Botha, Northcote-Green, Treviranus.
Replacements: Porecki, Elrington, Du Plessis, De Chaves, Gilsenan, Steele, Bell, Tikoirotuma.