Aurélien Collin has played in just one game for the Union this season, and it was for just one minute back in April. Before then, he hadn’t taken the field for the team since late September of 2019.

But right now, he might be making some of his most vital contributions in his three years in Philadelphia.

With up to 11 players potentially set to miss Sunday’s Eastern Conference final against New York City FC (3 p.m., 6abc and ESPN Deportes) due to health and safety protocols, Collin’s vast experience on big MLS stages is crucial for the locker room.

The 35-year-old French centerback is one of just two Union players with a MLS Cup winner’s ring, earned by scoring the tying goal and the winning penalty shootout kick in Sporting Kansas City’s 2013 triumph. This year, he has willingly become something of a player-coach, teaching the Union’s youngsters about life in the pros as much as he kicks a ball around in practice.

That has never been more badly needed than it is right now. Whether or not Collin plays or is just on the bench Sunday, calm heads are key as the Union try to simply assemble a game-day squad for the weekend.

“I think the club, Jim [Curtin], really taught us a philosophy, a way of playing,” Collin said. “Whoever is going to be on the field, we know that they’re going to give everything. If they follow our game model, I believe we will be good.”

» READ MORE: Eleven Union players are in MLS’ health and safety protocols ahead of the Eastern Conference final

‘The mentality that’s Philadelphia’

The 2013 ring isn’t Collin’s only career silverware. He also won a U.S. Open Cup with Kansas City in 2012 and a Supporters’ Shield with the New York Red Bulls in 2018, the latter right before joining the Union for the 2019 season. Between his tenures in Kansas City (2011-14) and northern New Jersey (2016-18), he played for Orlando City in its first season in MLS.

That adds up to 182 MLS regular-season games, 13 playoff games, 13 U.S. Open Cup games, and 17 Concacaf Champions League games across five forays in the continent’s biggest club tournament.

So he has seen a lot. And in his current team, he sees the ability to survive this latest stunning plot twist.

“The last three seasons, we’ve been seeing young players step up and playing well, and the other ones came [in] a little bit older and keep improving,” Collin said. “Jim did everything he could. And whoever’s going to be on the field, I would say that we know that they’re going to respect the mentality that’s Philadelphia, that they will give everything they have.”

It helps, he later added, that Curtin “gives a lot of freedom to his players” while also building strong locker room chemistry.

“Guys coming from everywhere in the world, young [and] older,” Collin said. “One of the keys to winning is we understand that we’re all together.”

» READ MORE: An 18-year-old with ice in his veins: Jack McGlynn was the Union’s penalty kick sensation

The Champions League earlier this year also played a big role. Not only was it the Union’s first foray in the competition, it took them to two of the continent’s most famously hostile venues: the bandbox home of Costa Rica’s Saprissa and the towering spectacle of Mexico’s Estadio Azteca.

“When we had to go to Costa Rica, the guys were up to the challenge,” Collin said. “So I think everybody’s ready.”

And while, as he put it, the Union “went through América” unsuccessfully, the semifinal series against Concacaf’s biggest club remains the biggest prize the Union have earned and the biggest test they’ve faced.

Win this weekend, though, and it will be time for new space on the mantle.

An opponent with ‘an identity’

As shorthanded as the Union might be Sunday, NYCFC will also be below full strength. The Pigeons’ star striker, Valentín Castellanos, is suspended after earning an ejection for two yellow cards in New York’s upset of record-setting Supporters’ Shield winner New England in the conference semifinals.

Until the Union’s outbreak arose, Castellanos’ absence was set to be the game’s biggest storyline. It still has plenty of the Union’s attention.

“New York City FC is a team that has an identity, like us, whenever they step on the field,” Collin said. “Of course Castellanos is a big piece, but we don’t worry a lot about who’s going to be on the field. We know the way they’re going to play, and when you look at the last game, they were amazing.”

» READ MORE: Eleven key games in the Union's run to the Eastern Conference final

Given all the absences, it won’t be surprising if the game is rather defensive.

“The first 15 minutes [are] going to be very important for us, and then after we have to make sure that we don’t stretch out the lines too much because New York is very good technically with the ball — and now they’ve become a team that is very good at counter-pressing,” Collin said. “Of course, as Jim always says, defense wins championships. So we’re going to have to be like the last two games, and like all season, very good defensively, and we’ll be OK.”

That doesn’t mean it will be easy. And just because Collin has scored a title-winning penalty in a shootout doesn’t mean it was easy for him to watch the Union’s shootout against Nashville.

“It was very, very stressful,” he said.

And yet...

“We have young players that are not scared,” he said. “When you think too much during PKs, maybe sometimes it’s an issue. ... Jack McGlynn’s PK was amazing. So, we’re ready.”

Whatever happens Sunday, it’s clear that the Union have grown in stature this season to a degree that they never have before. Collin has seen it in many different ways, working with his teammates while studying to earn his U.S. Soccer Federation “B” coaching license. And he has come to like Philadelphia quite a bit, too.

“You come to a city and you have two options: You make yourself at home or you don’t,” he said. “Some cities, it’s much easier than others. But Philly is a very easy city to make yourself home [in]. Old architecture, a lot of history, museums, good food. This is what I like.”

He likes winning soccer games, too, which his club has been doing. Now to see if it can continue.

» READ MORE: Win or lose, Subaru Park on Sunday will prove Philly is also a soccer town | Kerith Gabriel

» Join The Inquirer’s soccer staff for live coverage of the Union’s Eastern Conference final showdown with New York City FC on Sunday in Union Gameday Central. Kickoff is set for just after 3 p.m.