The extent of Dan Carter's leg injury should be known today.

The Crusaders medical staff are expected to re-examine Carter's lower right leg, which he injured during last Friday night's 20-10 loss to the Rebels at AMI Stadium, and only then will coach Todd Blackadder have an idea of whether the first five-eighth will be fit for next Saturday night's match against the Highlanders in Dunedin.

Following the Super Rugby opener Carter was optimistic the soreness below his knee was not a major issue and explained away the problem as being a "dead leg". He played on in the hope the pain would ease.

Clearly, however, he wasn't right; an attempted grubber was blocked and Rebels halfback Nic Stirzaker raced away to score the match-winning try.

Carter's injury is in the same area as the bone fracture he suffered during last year's Super Rugby final.

"The only way we will really know [if he will be fit to play the Highlanders] is if we can do a proper assessment," Blackadder said. "At the moment he feels the [injury to the] leg isn't overly serious and we will just see how it goes. We have a little bit of time."

Although Carter's experience should ensure he is a near-certain selection for the All Blacks' World Cup squad later this year, he cannot take it for granted.

Coach Steve Hansen started Beauden Barrett and Aaron Cruden ahead of Carter in the crunch matches against Wales and England on last year's northern tour and Colin Slade is also a competent No 10.

Blackadder knows there would be little point starting Carter in Dunedin if he isn't fully fit. He also has the luxury of shifting Slade to first-five because All Blacks fullback Israel Dagg is expected to return from his extended off-season break.

Given the poor performance of Crusaders backline - the inability to pass under pressure or catch the ball was excruciating to watch - against the Rebels, Blackadder may be tempted to rush wing Nemani Nadolo back.

However, that appears unlikely because the Crusaders have not yet got their hands on the big Fijian, who has just finished playing in Japan, and will want to assess his fitness.

Blackadder said it was too soon to discuss any potential selection changes but with loosehead prop Joe Moody having such a quiet game against the Rebels, he could bring Wyatt Crockett in.

Unlike his locking partner Luke Romano, who was fizzing for action, lock Dominic Bird was nowhere near his best.

No 8 Jordan Taufua showed plenty of desire and vigour when he replaced Luke Whitelock in the second half and his ball carrying could add more punch to a side that simply looked flat.

"We are not panicking by any means but we are certainly not satisfied," Blackadder said. "If you don't get a change in behaviour then questions have to be asked. "There were a few guys who were outstanding but we just didn't perform as a team [and] that is just unacceptable."