Tupai starts as injury-hit Saints make eight changes against Leinster
Connor Tupai will start for Saints at the Aviva Stadium on Saturday evening (kick-off 5.15pm).
The scrum-half, who only turned 20 last Sunday, comes in for his first Champions Cup start and seventh Saints appearance in all, replacing Cobus Reinach who is ruled out with the knee injury he picked up last weekend.
James Mitchell takes Tupai's place on the bench with Saints now missing three scrum-halves due to injury. Alex Mitchell and Henry Taylor are the others to be sidelined.
Tom Wood will make his 200th Saints appearance as he skippers the side from the back row.
Lewis Ludlam is at No.8 for the first time since making his Saints debut, with Teimana Harrison handed a well deserved weekend off.
Alex Coles starts in the second row in place of Alex Moon, who is ruled out with the head injury he sustained in last weekend's 43-16 defeat to Leinster at Franklin's Gardens.
Paul Hill starts as he makes his 100th Saints appearance at tighthead, while Francois van Wyk and Michael van Vuuren join him in a fresh front row.
Andy Symons returns to the backline, coming in for the rested Rory Hutchinson at inside centre, while Tom Collins is also given a breather as Ollie Sleightholme starts at 14.
Fiji hooker Sam Matavesi is set to make his Saints debut from the bench, having recently joined the club from Cornish Pirates, with Mike Haywood rested.
Saints have a lengthy injury list but Harry Mallinder and George Furbank are no longer on it.
Reece Marshall (hamstring), Reuben Bird-Tulloch (hand), Taylor (thumb), Ben Franks (elbow), David Ribbans (back), James Fish (head), Owen Franks (hand), Courtney Lawes (hamstring), Moon (head) and Reinach (knee) are the ones sidelined.
Leinster have made five changes to their side, with fly-half Jonny Sexton one of the men ruled out.
Hooker Ronan Kelleher is also missing, but Leinster are able to bring in the likes of James Tracy and Ross Byrne.
Tadhg Furlong and Scott Fardy, who were on the bench last weekend, come in for Andrew Porter and Devin Toner respectively.
Luke McGrath comes in for Jamison Gibson-Park at scrum-half.
Leinster: Larmour; D Kearney, Ringrose, Henshaw, Lowe; R Byrne, McGrath; Healy, Tracy, Furlong; Fardy (c), Ryan; Ruddock, van der Flier, Doris.
Replacements: B Byrne, E Byrne, Porter, Toner, Deegan, Gibson-Park, Frawley, R Kearney.
Saints: Tuala; Sleightholme, Proctor, Symons, Naiyaravoro; Biggar, Tupai; van Wyk, van Vuuren, Hill; Ratuniyarawa, Coles; Wood (c), Gibson, Ludlam.
Replacements: Matavesi, Waller, Painter, Bean, Tonks, J Mitchell, Grayson, Dingwall.