BRISBANE, Australia (AP) — The Matildas missing out on the knockout rounds of the Women's World Cup barely factored into pre-tournament reckoning in Australia.

The prospect of star striker Sam Kerr leading Australia to unprecedented heights was the focus of attention. But an upset 3-2 loss to Nigeria has set up what is essentially a must-win showdown for Australia against Olympic champion Canada on Monday.

With a win, Australia will advance to the round of 16 for the fifth consecutive time. A loss could result in Australia becoming the first host nation eliminated in the group stage of a Women's World Cup (co-host New Zealand is also in danger of missing out). A draw would have Aussie hopes hinging on Ireland beating Nigeria.

The scenario has unfolded all without Kerr playing a minute of her home tournament so far because of a calf muscle injury sustained on the eve of Australia's opening 1-0 win over Ireland last week in front of almost 76,000 fans in Sydney.

Steph Catley, deputizing for Kerr as Matildas captain, summed up the loss to Nigeria succinctly: “This was a massive opportunity for us that we’ve obviously let slide."

Though the Matildas controlled 64% of possession and had 28 shots on goal — including eight on target — they squandered key scoring opportunities and had costly defensive miscues.

“We created a lot of opportunities that we could’ve finished,” Catley said. "We weren’t patient enough, and we weren’t clinical enough.”

Head coach Tony Gustavsson echoed those sentiments, and acknowledged Australia doesn't have much time to make adjustments on the run.

The Australians had lost only one of their previous 11 matches before the Nigeria game, although they've struggled with injuries since the start of the tournament.

Chelsea star Kerr missed the first two games and isn't certain of returning to take on Canada. Manchester City forward Mary Fowler missed the Nigeria match with a concussion, also picked up in practice.

Kerr is Australia’s all-time leading goal scorer with 63 goals in 121 games, and its undisputed star.

“I know it’s going to be tight,” Gustavsson said of Kerr’s availability for the Canada match. “I most likely will not get the confirmation on that until the night before the game.

"It might even be where we need to test her to see if she can play on game day. That’s how tight it is.”

He knows Kerr will be desperate to get her first minutes, knowing her country needs her.

“That’s going to be her mindset," Gustavsson said. "And that’s what I love with Sam.”

The absence of Kerr and two other forwards has seemingly thrown tactical planning into disarray.

With the home team down 3-1 and desperate for goals late against Nigeria, Gustavsson introduced defender Clare Polkinghorne in the 81st minute and midfielder Alex Chidiac in the 85th minute in an attempt to spark the Matildas’ offense. Alanna Kennedy’s stoppage time goal narrowed the margin, but it was too little, too late.

Gustavsson was asked about his decision to wait until so late in the game to make changes.

“I think that’s a fair question and that’s something I need to look at as a coach,” Gustavsson said. “Did I find the right timing for the subs? We did get a massive effect positively when we did it. Did we get that because I did it in the right moment or should I have done it earlier?”

With the nature of the “day-to-day” injury status of Kerr and Fowler, Gustavsson could elect to make more tactical changes against Canada. One player who could see increased minutes is Chidiac, who impressed her coach in her limited time against Nigeria.

Chidiac “came in and was that game changer,” Gustavsson said. “She was upset afterwards that she didn’t score but I said ‘Hey, you were brilliant. When you came in you were that game changer.’”

The Matildas will again be forced to lean on depth for production against a team that only needs a draw to advance. The Canadians are coming off a 2-1 win over Ireland following a 0-0 opener against Nigeria. Canada and Nigeria are tied for the Group B lead with four points, one clear of Australia.

“We’ve just got to move on as quick as possible,” Catley said. “Our backs are up against the wall now. It’s not how we would’ve liked it, but nothing good comes easy."

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Luke Winstel is a student at the University of Georgia’s Carmical Sports Media Institute.

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AP Women’s World Cup coverage: https://apnews.com/hub/fifa-womens-world-cup and https://twitter.com/AP_Sports