Ronaldo departs as the most capped player and leading goalscorer in international football history, having recorded 146 goals in 234 appearances. His international career, which began in August 2003, was highlighted by Portugal’s triumph at the 2016 European Championship.

The retirement follows a period of significant tension between the veteran forward and Portugal head coach Jorge Jesus. Ronaldo had been suspended from international duty during the previous break after leaving the training camp early following a disagreement regarding his playing time.

The dispute reportedly intensified after Ronaldo was told he would not start a recent Nations League match. The forward subsequently left the stadium immediately at the final whistle, bypassing the traditional post-match acknowledgement of the travelling supporters.

In a statement released via social media, Ronaldo reflected on his tenure with the national team. "To the Portuguese people, the day has come to return the No. 7 jersey of the national team," he said.

"I never felt it belonged to me alone but for 23 years I had the privilege and responsibility of wearing it, defending it and carrying it with me into stadiums all around the world," he added.

Ronaldo acknowledged that the decision was difficult to make, noting that it was reached with both his mind and his heart. He concluded by stating that his journey, which began over two decades ago, had reached its natural end.

The announcement leaves Portugal to transition into a new era without their long-time captain. The team is expected to name their squad for the upcoming international window on Friday, marking the first time in 23 years that Ronaldo will not be included.

The first leg, held at Inver Park on Friday, saw Portugal justify their status as favourites by securing a comfortable four-goal victory. Following that result, McArdle initially suggested that the prospect of reaching the tournament had shifted from improbable to impossible.

However, speaking ahead of Tuesday's return fixture in Portimao, the 48-year-old manager expressed a more optimistic outlook. He believes that an early goal could shift the momentum and potentially change the complexion of the tie entirely.

"We're always positive, and from that perspective it's another opportunity for us to learn and put ourselves toe-to-toe with them," McArdle said. "If we end up in front first or how the game goes, it could turn back from impossible to improbable again."

In the first encounter, Portugal established dominance early through an opening goal from Telma Encarnacao. Jessica Silva doubled the lead shortly after, and a misfortune for Rebecca Holloway, who scored an own goal, left Northern Ireland trailing by three within the first half-hour.

Despite the heavy scoreline, Northern Ireland showed signs of improvement after the interval. They appeared to be the stronger side for a period following a red card for Portugal's Catarina Amado, yet they were unable to convert their pressure into a goal.

The visitors ultimately capitalised on their opportunities, with Fatima Pinto adding a fourth goal from long range to seal the victory. McArdle acknowledged that his side struggled to manage the gaps between their centre-backs and the inexperienced full-back pairing of Jane McMaster and Emily Cassap.

"The immediate reflection was misfortune with the scoreline, and how it was a bit harsh," McArdle noted regarding the first leg. "Reflection-wise we still feel that way, however there's areas that we need to improve upon before the game."

The manager remains without striker Cora Chambers for the second leg, as she was sent off during the closing stages of the match in Larne. Otherwise, the squad has a full complement of players available for selection in Portugal.

The first leg saw McArdle hand international debuts to three players: Linfield defender Jane McMaster, Sparta Prague forward Kess Elmore, and 16-year-old Cliftonville midfielder Charlotte Havern. These selections reflect the manager's commitment to integrating youth into the senior setup.

Even if Northern Ireland manage to produce a significant turnaround in Portimao, their path to the 2027 Women's World Cup remains exceptionally difficult. The winners of this tie are expected to face Iceland, who currently hold a 4-0 lead over Croatia in their own play-off.

Furthermore, due to their current UEFA ranking, Northern Ireland would likely face an additional inter-confederation play-off even if they were to progress through the next round. The tournament itself is scheduled to take place in Brazil next summer.

McArdle, who took charge of the team in March, emphasised that his focus extends beyond the immediate challenge of the World Cup qualifiers. He believes the team is making tangible progress during his six-month tenure.

"You've seen that with the new players, the amount of debutants and the amount of youth players that come into the squad over the three camps I've been involved now," the manager explained regarding the team's development.

The manager highlighted that the squad is currently in a strong position as they look toward future competitions. Following the conclusion of the current play-off campaign, the team will shift their attention to qualifying for the European Championships.

"We're now in a really strong place, and from the next window onwards we'll start to prepare and focus on trying to qualify for the Euros," McArdle added. "That'll be the most important piece after Tuesday, but we'll have one last swing."

The second leg in Portimao is scheduled for Tuesday evening. Fans in Northern Ireland can follow the action via BBC iPlayer, with live commentary and updates also available through the BBC Sport website and mobile application.

The match represents a significant learning opportunity for the younger members of the squad as they gain experience against high-level international opposition. McArdle is keen to see how his players respond to the challenge of playing away from home.

As the team prepares for the final whistle of this particular campaign, the focus remains on maintaining a professional standard. The coaching staff is looking for a disciplined performance to close out the current cycle of matches.

Ultimately, while the odds remain heavily stacked against them, the Northern Ireland squad is determined to end the series on a positive note. The match serves as a final test of their resilience before the next phase of international football begins.