The Blues' injury woes have struck again, with experienced loose forward Justin Collins ruled out of their vital Super 14 rugby match against the Brumbies.

The Blues head into Saturday's match in Canberra in eighth place on 31 competition points with two round-robin games remaining, one point behind the seventh-placed Brumbies.

Both still have a mathematical chance of forcing their way into the semifinals, and the loser of Saturday's match will almost certainly have their season ended.

The Blues, coming off losses to the Reds and Hurricanes, have had a number of injuries and with them seem to have come problems with defence, and coach Pat Lam was hoping blindside flanker Collins would return this week and add some bite in that area.

But after reporting a persistent headache after Thursday morning's training, Collins was replaced by Peter Saili, with Counties Manukau newcomer Andrew Van der Heijden on the bench.

Van der Heijden could yet start at lock as Kurtis Haiu could miss the game while waiting for his partner to deliver their second child.

Lam said the closest the Blues got to having a full-strength team this year was on February 28 against the Stormers, a match they won 14-8 in Cape Town.

"Probably our biggest defensive effort was the Stormers game, you look there you had Blackie, you had Kaino and you had Collins playing, an All Black front row, plus Boric and Haiu," Lam said.

"You can't underestimate the difference experience makes when it comes to tight games, particularly around defence, so having Col back, that's one thing he's really committed around that area and passionate about defence."

All Blacks locks Ali Williams and Anthony Boric are also missing, though balancing that slightly is the return of All Blacks tighthead prop John Afoa, who will bolster the scrum and tight work.

Winger Rene Ranger and centre Anthony Tuitavake are also battling injuries though they both ran at 80 per cent fitness and it is hoped they will be fit.

With the Blues four points away from the top four and with several teams above them playing against semifinal rivals at some stage in the final two weeks, a semifinal position is not impossible but they are likely to need a win with a four-try bonus point to give themselves a chance.

Despite the injuries, Lam said the morale of the team was high and they were pleased the Blues board gave them permission to fly out on Thursday rather than Friday.

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