Jamie Gibson and Luther Burrell will both be missing when Saints travel to Wasps for a crucial Aviva Premiership clash on Sunday (kick-off 3pm).
Gibson rolled his ankle and was forced off at the break in last weekend’s 29-23 win against Harlequins at Franklin’s Gardens.
The consistent flanker had previously only missed one game - the home defeat to Wasps in January - since joining from Leicester Tigers last summer.
Burrell took a bang to the head in the victory against Quins and was replaced on 67 minutes by Harry Mallinder, who went on to score the bonus-point try.
Mallinder starts in place of Burrell at 12 this weekend, while Sam Dickinson replaces Gibson in the back row.
That means Tom Wood, who will skipper Saints, shifts to six and Teimana Harrison, who was at No.8 last weekend, is in the seven shirt.
The other change in the pack sees Christian Day return after he was ruled out with a throat abscess last weekend.
The lock was forced to make a trip to A&E but he is well again now, replacing James Craig in the second row.
Kahn Fotuali’i is another man coming in as he replaces Lee Dickson at scrum-half.
It will be Fotuali’i’s first start since New Year’s Day, when he pulled his hamstring in the win against Exeter Chiefs.
Tom Collins, who scored the winning try in Saints’ 27-23 friendly success against Wasps at the Ricoh Arena back in October, gets a place on the bench.
Meanwhile, Wasps have recalled Wales lock Bradley Davies, who was given last weekend off following Six Nations duty.
Craig Hampson, who impressed on his Premiership debut against Newcastle Falcons last weekend, starts at scrum-half with Dan Robson and Joe Simpson both out.
Frank Halai returns to the team, taking his place on the wing.
Wasps: Miller; Wade, Daly, S Piutau, Halai; Gopperth, Hampson; Mullan (c), Johnson, Cooper-Woolley; Launchbury, Davies; Young, Smith, Hughes.
Replacements: Festuccia, McIntyre, Cittadini, Myall, Haskell, Stevenson, Jackson, Tagicakibau.
Saints: Foden; K Pisi, G Pisi, Mallinder, North; Myler, Fotuali’i; A Waller, Haywood, Brookes; Lawes, Day; Wood (c), Harrison, Dickinson.
Replacements: Marshall, Ma’afu, Hill, Craig, Fisher, Dickson, Hanrahan, Collins.