Horwill suffered a hamstring injury two weeks ago which ruled him out of the home Rugby Championship tests against South Africa and Argentina.
The Wallabies missed both his leadership and physicality in the 38-12 drubbing at the hands of the Springboks and could do with both back for the return match in Cape Town on Sept. 28.
Australia go on from South Africa for a re-match with Argentina, who they edged 14-13 at the weekend, and McKenzie said Horwill would have to be fit to train if he was to embark on the flight to Cape Town.
"There's no evidence to say (he) wouldn't be fit by the weekend," McKenzie told reporters in Perth before the squad dispersed for a week off.
"I think James would know he has to be right to train 100 per cent on Saturday. That's what we'll look at and we'll work it out. I think he is tracking well."
When fit, Horwill has been Australia's captain since replacing Rocky Elsom in a shock move on the eve of the 2011 World Cup in New Zealand.
Having also led the Queensland Reds to Super Rugby success for the last few years under McKenzie, his place as team leader looked assured when Robbie Deans resigned in the wake of the British and Irish Lions series defeat.
McKenzie, though, has displayed a distinct lack of sentiment with regard to his former Reds players since taking the reins at the Wallabies.
Firstly, against all predictions, he failed to restore flyhalf Quade Cooper to a starting role for the first two tests of the championship against New Zealand, which both ended in defeat.
In an even more stunning decision last week, McKenzie dropped scrumhalf Will Genia to the bench for the match against the Pumas in Perth.
Given those decisions, it should come as no surprise that McKenzie would not confirm that Ben Mowen would hand back the captaincy when Horwill returns.
"I haven't thought about it," he added. "I'll work out where he is up to on the injury. I have to see if he is fit enough to join the group first."
Given the problems at the scrum that have been exposed by the Springboks and Pumas over the last two weeks, it was no surprise either to hear that 59-cap loosehead prop Benn Robinson was under consideration for a return for the two-match tour.
Robinson, criticised by some for his lack of work rate around the park and dumped from the original squad for the championship, was replaced in the number one shirt by James Slipper for McKenzie's first four tests.
"We know what he's capable of and has a lot of experience so he's never out of your thinking," former test prop McKenzie said. "It's just a question of the guys you've got and whether you're happy with how they're travelling."