Saints director of rugby Jim Mallinder said that his team will be taking nothing for granted this week.
With five wins from as many matches, Saints have made their best ever start to a premiership season. But Mallinder said they will be on their guard against a London Irish outfit which has plenty of international talent available and won last time out at home.
"We have had a promising start to our season, but we know that if we lose concentration we will be in danger of losing our record," he said.
"London Irish have plenty of danger in all areas of their team and their goal kickers will punish us if we lose our discipline in our own half.
"Last Friday's game against Wasps was just about our most complete performance of the season, and we will be looking to build on that tomorrow. We need to maintain control, impose ourselves and take our chances, and then we will have the result we want."
Meanwhile, George Skivington, Bryn Evans and Matt Garvey will all start amongst the forwards for London Irish.
Skivington and Evans will form the second row combination with Garvey moving to blindside flanker in place of Declan Danaher.
Steven Shingler starts at full-back replacing Tom Homer. Evans will captain the side in Danaher's absence.
London Irish director of rugby Brian Smith expects a tough encounter against Saints.
"Northampton have enjoyed a good start to the campaign," he said.
"They are a quality team and this match will be a great test of our resolve and character.
"The last time we were at Madejski Stadium we played well and enjoyed a good win over Bath. We'll need to perform at the same level tomorrow to claim a win and I believe we can do that."
London Irish: 15 Steven Shingler, 14 Topsy Ojo, 13 Jonathan Joseph, 12 Sailosi Tagicakibau; 11 Marland Yarde, 10 Ian Humphreys 9 Tomás O'Leary, 8 Ofisa Treviranus, 7 Jamie Gibson, 6 Matt Garvey, 5 Bryn Evans (c), 4 George Skivington 3 Halani Aulika, 2 David Paice, 1 Max Lahiff.
Replacements: 16 Shaun Malton, 17 Jerry Yanuyanutawa, 18 Alan Cotter, 19 Kieran Low, 20 Chris Hala'ufia, 21 Guy Armitage, 22 Shane Geraghty, 23 Jack Moates.
Northampton: 15 James Wilson, 14 Ken Pisi, 13 Dom Waldouck, 12 Luther Burrell, 11 Vasily Artemyev, 10 Stephen Myler, 9 Lee Dickson, 8 Phil Dowson (c), 7 Tom Wood, 6 Courtney Lawes, 5 Mark Sorenson, 4 Samu Manoa, 3 Brian Mujati, 2 Mike Haywood, 1 Soane Tonga'uiha.
Replacements: 16 Ross McMillan, 17 Alex Waller, 18 Paul Doran Jones, 19 Teimana Harrison, 20 Rhys Oakley, 21 Martin Roberts, 22 Ryan Lamb, 23 Tom May.
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