Dagg faces surgery
Dagg had an MRI scan, which has confirmed a PCL and lateral meniscal injury.
He has been seen by a specialist, who recommended a small operation to assist his recovery.
Dagg is expected to be ready to return to play in approximately six weeks.
The Crusaders, who face the Blues in Christchurch in a Super Rugby Round Four match on Friday, will also be without the services of two other players.
Seta Tamanivalu is progressing well after sustaining a right upper hamstring injury against the Reds last week.
His return to play is expected to be in the vicinity of four weeks.
Digby Ioane has also been ruled out with injury this week, after sustaining a minor hand injury.
The injury will be assessed early next week, before a decision will be made about his availability for the following weekend's game against the Western Force.
* Meanwhile Crusaders coach Scott Robertson has made seven changes to the starting side that beat the Reds last weekend.
Owen Franks returns to the No.3 jersey, while Jordan Taufua and Jed Brown join Whetu Douglas in the loose forward trio.
Bryn Hall will start at scrumhalf this week against his former team, with Mitchell Drummond on the bench.
Manasa Mataele will make his Super Rugby debut, replacing his injured uncle Seta Tamanivalu at No.14.
George Bridge takes the other wing, with Digby Ioane also ruled out after injuring a finger.
David Havili steps into the fullback position, with Israel Dagg out of contention after injuring his knee.
Wyatt Crockett and returns to play this week off the bench, providing prop cover alongside Michael Alaalatoa. Pete Samu provides loose forward cover, and Sean Wainui will cover the backs.
Crusaders: 15 David Havili, 14 Manasa Mataele, 13 Jack Goodhue, 12 Ryan Crotty, 11 George Bridge, 10 Mitchell Hunt, 9 Bryn Hall, 8 Whetu Douglas, 7 Jed Brown, 6 Jordan Taufua, 5 Sam Whitelock (captain), 4 Scott Barrett, 3 Owen Franks, 2 Codie Taylor, 1 Joe Moody.
Replacements: 16 Ben Funnell, 17 Wyatt Crockett, 18 Michael Alaalatoa, 19 Luke Romano, 20 Pete Samu, 21 Mitchell Drummond, 22 Marty McKenzie, 23 Sean Wainui.
Date: Friday, March 17
Venue: AMI Stadium, Christchurch
Kick-off: 19.35 (06.35 GMT)
Referee: Brendon Pickerill (New Zealand)
Assistant referees: Angus Mabey (New Zealand), Cam Stone (New Zealand)
TMO: Aaron Paterson (New Zealand)
