Israel Dagg cuts a dejected figure after injuring his right knee against the Reds on Saturday night.

The Crusaders aren't any wiser on the severity of Israel Dagg and Seta Tamanivalu's leg injuries.

Both All Black backs will definitely miss the unbeaten Crusaders' clash against the Blues at AMI Stadium on Friday night, but beyond that not much is clear.

Dagg and Tamanivalu were forced off the field in the first half of the Crusaders' 22-20 come from behind Super Rugby victory over the Reds in Brisbane on Saturday.

CHRIS HYDE Crusaders' fullback Israel Dagg looks set to be sidelined for the next few matches at least after a knee injury on Saturday.

Tamanivalu, who suffered hamstring damage, was a spectator on Monday as the Crusaders dodged the heavy rain outside for a light indoor training run at the Apollo Projects Centre in Ilam. Dagg was scheduled to undergo an MRI scan for his injured right knee.

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"We're no further ahead than we were [on Sunday] as to how long they're going to be out for and how quickly they'll heal," Crusaders' assistant coach Brad Mooar said.

"Whether that's going to be two weeks, four weeks or six weeks, whatever, we'll find out when we're told."

Dagg cut a forlorn figure, leaving the match in the 10th minute after injuring his knee as he scrambled to grab a kick.

It was a crushing blow for the 61-cap All Black, who had made a fine start to the Super Rugby season against the Brumbies and Highlanders in the opening two rounds.

"He's going to have a look with the specialist and they'll have a scan and that's a great way to rule things in or rule things out."

Tamanivalu's injury might not be as bad as first feared. Mooar said the blockbusting wing was "a pretty quick healer" and was showing promising early signs.

Tamanivalu has made a solid start to his Crusaders' career since moving south from the Chiefs, dotting down for tries against both the Brumbies and Highlanders.

"Already in two days, he's moving a lot more freely than he was on Saturday night or Sunday as we were coming back. We'll see what happens."

Fullback David Havili and All Blacks' loose forward Matt Todd, who both missed the Reds' match, took part in Monday's training session. Mooar said they would both come into contention for the Blues' match.

The Crusaders have proved comeback kings over the past two weeks, fighting back from 27-6 down to beat the Highlanders 30-27 in Dunedin.

Against the Reds, they trailed 17-0, but dragged themselves off the canvas, winning through a 80th minute penalty from rookie first five Mitchell Hunt.

Mooar was quick to point out the Crusaders couldn't keep giving the opposition a sizeable lead. They were addressing all areas of their pre-game routines and general play to work out why they weren't firing.

"Let's not get too caught up in the outcome. We started extremely well against the Highlanders and we started very well against the Brumbies. We've had flat patches we've got to get right."

Crusaders' midfielder Ryan Crotty said their start against the Reds was a concern and had been discussed in the debrief.

"I think the weekend was one-off . . . I thought we started really well against the Highlanders. It was probably more of the second half of the first half [against the Highlanders] where we fell away and lost momentum from giving away penalties."