Petrie fractured the fifth metatarsal in his left foot ahead of round one, and had surgery last Monday to have a screw inserted in the bone.
He had his plaster cast removed on Tuesday and will spend three weeks in a moon boot, the first of those with the aid of crutches, before he can resume walking as normal.
Petrie said the screw was insurance because his injury could reoccur if it didn't heal properly.
"It's a titanium screw, so it's not going to break again," he said. "The break still does need to calcify and heal itself.
"I can categorically [say] there's only one break, the operation went very well, the screw's in there and it's going to take a few weeks to heal. That's it.
"If anybody believes anything different or wants to make up anything different, come down to training on Friday and I'll show you my x-rays. The proof will be there."
Petrie, who was suspended for the first two rounds of the season, had felt some soreness in the area for around 10 days before his foot cracked in the last drill of a training session on March 23.
The 27-year-old initially thought he would miss six weeks, but sensed that was the best-case scenario.
"They were the initial thoughts of the medical staff, is that you can be back in six weeks with natural healing and it healing really well," he said.
"We're leading into round three this week and I don't think I'll be able to run on it until at least round seven or eight.
"I need a couple of weeks of training so I don't get any soft-tissue injuries after that, which is pushing it out to round eight or nine."
Petrie admitted it was frustrating to watch his teammates from the sidelines at any time, let alone for their 104-point hammering from St Kilda last weekend.
He said the Roos' poor starts in both of their games had thrown them straight to the ropes.
"The boys gave up an eight-goal lead against Port Adelaide and did the same against St Kilda," he said. "[It's very difficult] to win a game when you do that at the start.
"A lot of people have been cursing us about how bad we played, but we can't forget at the same time how good St Kilda is," he added.
"They're a side who I think over the next three years will be big contenders for grand finals and premierships. They're in their peak period as a club.
"That's not to say we couldn't have performed better. Our effort was average."
Petrie said David Hale had done a great job so far but he was keen to see fringe players Aaron Edwards and Josh Smith also given their opportunities in the forward line.
