McKenzie said he was undecided what kind of game plan they would take into the Rosario clash against Argentina on Sunday, although he hoped the side could successfully execute both as required.
"You saw against the Springboks two halves of footy: a kicking half and a running half," said McKenzie.
"Clearly if we're playing running footy Will's our best exponent but Whitey is with our kicking game so it depends on how we want to pitch the game."
He recognised that Genia, who has captained the side, also offered unparalleled experience which would be vital in an Argentine rugby cauldron.
"Everyone knows the capability of Will. I know it better than anyone after coaching him in plenty of games," McKenzie said. "You've got to make decisions on what's going on at that point of time."
As for a swag of changes to the squad, McKenzie said the answers lay in the players he had.
"Tell me who the other people are who are going to break the game open and suddenly give us the silver bullet.
"I think we've got the best players available."
Australia are ahead of last-placed Argentina on the Rugby Championship ladder going into the final round but by only two points.
The Wallabies have four points thanks to their sole win, over the Pumas in Perth, while the Pumas have no wins but two bonus points.
The Pumas put world champions New Zealand under the pump in their weekend game, leading early in the second half before the All Blacks fired up for a 33-15 victory which puts them in a strong position to clinch the title against South Africa in Johannesburg this weekend. McKenzie, who has stayed remarkably sanguine despite having only one win in the Rugby Championship, said he hadn't had a chance to watch that clash but didn't expect the Pumas to stray far from their usual physical forward-focused style.
McKenzie didn't play a test in Argentina during his 51-cap Wallabies career but was an assistant coach with the Australian side who beat the Pumas in Buenos Aires in 2002.
"It's the Latin mentality that scrummaging's very personal and there's a lot of prestige and pride that goes with that," he said. "There's not one team that says going to Argentina ... is an easy task."
- AAP