Lima Sopoaga is another option as the All Blacks cover for the loss of Aaron Smith, who has returned to New Zealand to face his well-publicised misconduct hearing.
Coach Steve Hansen said it was unlikely another halfback would be brought over to South Africa in the event of an injury to either of their specialists, and that the side always prepared for emergencies.
"We've been training another halfback in the squad," Hansen said. "There's two scenarios. Obviously if we lose one at training we could possibly bring one over really late but if not we would bring Damian in at halfback. He trained there this morning when we did a clarity run.
"If we lost both halfbacks as we have done at the past when we used Sladey [Colin Slade] a few years ago over here, then Lima will go there.
"It's like most things, we try to plan for most what-ifs that occur. We don't always do we get them all covered but we're usually not too far away.
"Halfback is a specialist position so you have to have someone in your group that can jump in there if you lose both of them in a game."
Asked if the ability to play an extra position could be an added strength for McKenzie, who can play first-five and fullback, Hansen said: "I'd like to see him play No 10 before he starts playing No 9. If we get that part of it right then he might play him at No 9. He'd play anywhere, that kid."
The Chiefs 21-year-old, who weighs about 85kg, has the body shape and pace off the mark to slot into halfback without too many problems. He has not been included in the match-day squad, but would enter it should starting halfback Perenara be unavailable. Specialist first-five Sopoaga is on the reserves bench as cover for Beauden Barrett.
Hansen, who wouldn't elaborate on the Aaron Smith situation, said most scenarios were covered at training, including having halfbacks throw the ball into the lineout in the event the hooker was sent off.
The All Blacks, who arrived in Durban from Buenos Aires after 23 hours of travel, were happier at sea level compared with the high altitude of Johannesburg, where they usually play in South Africa.
"It feels different from a recovery point of view," Hansen said. "We've recovered a lot quicker which is nice. It's a matter holding the boys back at the moment rather than trying to build them up."
And he made no secret of the fact his team were gunning for the world record of 18 consecutive test victories. Should they beat the Boks on Sunday morning they will reach 17 in a row.
"It's like everything else - if you try to avoid it it creates more pressure so if you do talk about it and embrace it, it then becomes a challenge. Whether you're successful or not is irrelevant, that's the outcome. It's certainly been something that motivates this group.
''They want to be a team that's seen to be a great All Black side and to be a great All Black side you have to do things that other teams haven't done."