McCaw is likely to stay at No8 if Read is unavailable, with Matt Todd, who played well against the Force on the openside flank, staying in the No7 jersey.
When asked about the Crusaders' reliance on McCaw and Carter - the Force won the second half of the match 21-6 once the pair had been replaced by Luke Whitelock and
Tom Taylor respectively, Blackadder said: "Their influence is huge but also what they command from the guys around them. By taking them off, you're certainly taking your two best players off. The other guys go in there and do a good job, but it's probably the message it sends everyone else, we can take the foot off the gas ... we've got the game won.
"It wasn't the fact we weren't trying, we blew about six opportunities in the second half. If we had got those it would have been a different scoreline.
"I'm pleased where we are at, it gave the other guys game time. Luke will be better for that experience and so will Tom Taylor.
"We made a lot of changes and fell off the pace a bit but I felt the game was won at halftime.''
Blackadder said his players were looking forward to playing the Bulls at home in a knockout game, after losing to them at in Pretoria in similar stages in 2007, 2009 and 2010.
"I think Richie's lost three in knockout stages to the Bulls so we're pretty determined to do well.''
The Reds host the Sharks in Brisbane on Saturday night in the other qualifier match. The Stormers and Chiefs have a bye this weekend. The winners of the qualifiers progress to the semifinals.