Less than a month ago he was a virtual lock for a Kangaroos squad short on fire and infinitely short on brimstone.
Now he's barely a lock in a Toa Samoa side that can both secure what would be their first ever Four Nations final birth, as well as knock Australia out of a major tournament for the first time since 1954.
Having begun the Four Nations campaign in the No.13 jumper for his mother's nation, McGuire was a shock starter from dummy half in last week's pulsating defeat to New Zealand.
But the Broncos firebrand says he has nothing to prove to Australia – or coach Matt Parish, for that matter – in Sunday's must-win clash.
"We started [the game] with four ruck forwards to start with a bit more size there in the middle," he told NRL.com at a Toa Samoa fan day in Campbelltown on Thursday.
"New Zealand were a big side, so we just wanted to go with that and then after 20 minutes I just went to lock and then Pita [Godinet] came on and I just finished the rest of the game at lock. It's just about having those big bodies in the middle.
"I'd never done that before in first grade but it was a great opportunity for me to play in a different position and see how I go. I actually thought I went alright, so we just have to wait and see what [the] coach wants. It'll be interesting to see what he comes up with."
McGuire was considered by many to be a strong chance of making his Kangaroos debut after playing a part in the Prime Minister's XIII side that defeated Papua New Guinea 34-16 in Kokopo.
But the 24-year-old was overlooked for younger talents such as Dylan Napa and David Klemmer, the latter of whom made his debut against England last week.
"They went in the direction they wanted to go in and I wasn't a part of it, so that's fine. I don't have a point to prove," McGuire said.
"I just wanted to keep playing footy and I had the opportunity to keep doing it here, which I can't thank [coach Matt Parish] and Samoa enough for helping me do it. I'm really enjoying my footy at the moment and I can't wait to play next Sunday."
It was the second time McGuire had been overlooked by coach Tim Sheens after being left out of a similarly depleted squad for the corresponding tournament in 2011 having previously represented Samoa in 2010.
"It is what it is. It's the Australian team, it's the hardest to make in the whole world," McGuire said.
"Obviously I would've liked to be there, but I didn't get it and that's what it is. I have this opportunity now, it's been a blessing and I can't thank the team enough for letting me and I'll do everything I can this week to get the win."
Despite the disappointment of missing out on a maiden Kangaroos jumper, the Brisbane junior said the tournament was a huge opportunity for Origin hopefuls to showcase their abilities on a bigger stage.
After two games, McGuire tops the tackle count for the Four Nations with 86, while also leading his team in carries.
"Obviously in Origin you're playing against the best players in the world but if you can show that you can play some good footy here and hold your own, then it certainly wouldn't do your chances any harm," he said.
"It's a great opportunity for everyone here to showcase what you can do. A lot of players are playing for NRL contracts too, so it's just a good opportunity across the board for everyone to play some good footy and enjoy yourselves."