Hartley out of European quarterfinal
The Saints had been optimistic the hooker would return from the concussion he suffered in England's victory over France in Paris last month that saw them complete a Six Nations clean sweep.
But he was left out of Saints' matchday 23 confirmed on Friday along with prop Kieran Brookes and scrumhalf Lee Dickson, who both suffered head knocks during last weekend's defeat by Wasps.
Meanwhile, Wales wing George North, England back-row Tom Wood and No.8 Sam Dickinson are also sidelined, although England international Luther Burrell is back at inside centre following concussion.
By contrast, Premiership leaders Saracens are close to full strength, with England lock Maro Itoje – one of the stars of this season's Six Nations – fit following a knee injury suffered in a league win over Bath.
"We have lost our hooker Jamie George as well so all sides have to deal with injuries," said Saracens forwards coach Alex Sanderson.
"Hartley is huge for them, but Mike Heywood has been playing really well. Maybe not so much in his last game, but he was outstanding against Quins with some of his play around the field, his offloading and work over the ball.
"Northampton don't lose much around the field without Hartley, but as a leader and as an inspiration of course they miss him."
There are five English clubs in the last eight of European club rugby union's premier competition and another all-Premiership tie sees Exeter, with Australia's Lachie Turner at full-back, away to Wasps on Saturday.
The last time the clubs met at Wasps' Coventry home, Exeter back-row Thomas Waldrom helped himself to a hat-trick.
Waldrom, rather than a wing, currently leads the Premiership try-scoring charts with 13 so far this season, having topped the standings last term with 16.
Many of the former England loose forward's scores have come off the back of scrums or close-range drives.
"Physically, his shape does allow him to hold his feet," said Exeter coach Rob Baxter. "A taller, rangier guy could get lassoed and chopped down.
"He doesn't just do the same thing every time. There is a bit of variety to what he does.
"He also plays with a group of lads who know what he's going to do, and so there is a bit of a synergy there now to helping him over the line."
Wasps, European champions in 2004 and 2007, are set to be captained by England back-row James Haskell.
Double European champions Leicester round off English representation in the quarterfinals at home to Stade Francais on Sunday.
Northampton: 15 Ben Foden (captain), 14 Ken Pisi, 13 George Pisi, 12 Luther Burrell, 11 Jamie Elliott, 10 Stephen Myler, 9 Kahn Fotuali’i, 8 Teimana Harrison, 7 Ben Nutley, 6 Courtney Lawes, 5 Christian Day, 4 James Craig, 3 Paul Hill, 2 Mikey Haywood, 1 Alex Waller
Replacements: 16 Reece Marshall, 17 Campese Ma’afu, 18 Gareth Denman, 19 Victor Matfield, 20 Michael Paterson, 21 Tom Kessell, 22 JJ Hanrahan, 23 Harry Mallinder
Date: Saturday, April 9
Venue: Allianz Park, London
Kick-off: 17.45(16.45 GMT)
Referee: Jerome Garces (France)
Assistant referees: Mathieu Raynal (France), Pierre Brousset (France)
TMO: Eric Gauzins (France)
