Manchester United have famously boasted an academy graduate in every match-day squad for more than 80 years, and their upcoming Europa League tie pits them against a club who also pride themselves on producing homegrown talent.
United face Real Sociedad - in the neutral venue of Turin because of coronavirus restrictions - in the first leg of the last-32 clash on Thursday. They will come up against a club whose current first-team setup includes 16 of their own graduates.
Five of those - Jon Bautista, Jon Guridi, Andoni Gorosabel, Martin Merquelanz and Luca Sangalli - featured when La Real's under-19 side beat United 1-0 in the Uefa Youth League in 2013, while Alvaro Odriozola scored the winning goal and is now at Real Madrid.
Andreas Pereira is the only player still on United's books from that fixture, though the Brazilian midfielder is on loan at Lazio.
Ole Gunnar Solskjaer's side have plenty of Carrington-schooled talent, with the likes of Marcus Rashford, Mason Greenwood and Scott McTominay continuing a record that began in October 1937.
One player who spent time in the Premier League club's academy could even line up against them for the Basque outfit.
Adnan Januzaj, who arrived at United from Anderlecht as a 16-year-old, was tipped for greatness at Old Trafford after being promoted to the senior squad by Sir Alex Ferguson.
David Moyes gave the teenager his debut as a substitute in the Community Shield win over Wigan Athletic and Januzaj scored twice in a 2-1 victory against Sunderland on his first Premier League start.
The winger was awarded a five-year deal, scoring four times in total that season and registering six assists in all competitions, and was handed the number 11 shirt after Ryan Giggs retired.
That would be the peak of his rapid rise in England, though, and he has been talking to BBC Sport about how things went wrong for him after Louis van Gaal's arrival.
Could he return to haunt his former employers? The 26-year-old has made more than 100 appearances since arriving in San Sebastian, but has not been a regular starter this season, playing 12 times in La Liga, scoring twice and making one assist.
What to expect from Sociedad?
Sociedad's biggest threat is Spain international Mikel Oyarzabal, a player regarded as their most exciting product since forward Antoine Griezman, who is now at Barcelona.
Born in Eibar, halfway between San Sebastian and Bilbao, 23-year-old Oyarzabal arrived at La Real's academy from his hometown club in 2011 at the age of 14 and was handed his first-team debut by Moyes four years later.
Oyarzabal has been his side's best attacking outlet this season, scoring 10 goals in all competitions and laying on six assists.
"We have a style of play that favours the squad we have and suits everyone," explains Oyarzabal.
"What's more important is that whoever plays in the team, while still important, it is less important when the idea is clear and we know what we have to do."
The "idea" is a possession-based, attacking style of football that took Real Sociedad top of La Liga earlier this season, though they have now slipped to sixth.
As well as producing current stars such as Oyarzabal and 19-year-old winger Ander Barrenetxea - the club's youngest debutant in more than 80 years - breaking from the tradition of only using Basque players in 1989 has allowed La Real to fine tune their squad with talents from outside the region.
Sporting director Roberto Olabe, another former Sociedad player, has complemented the club's successful academy programme with smart recruitment, highlighted by the signing of David Silva from Manchester City on a free transfer this season.
Premier League fans will also recognise former Arsenal left-back Nacho Monreal, who grew up in nearby Pamplona and played for Osasuna, as did midfielder Mikel Merino before spells at Borussia Dortmund and Newcastle United.
La Real's recruitment is not limited to Spaniards, however, with 21-year-old Sweden forward Alexander Isak, who has been compared to Zlatan Ibrahimovic, scoring 16 times last season as the Basque outfit secured a Europa League spot and reached the final of the Copa del Rey.
Producing talent the La Real way
Few top European clubs have put as much emphasis on integrating young players into their side as La Real, whose unique approach includes only signing academy players at under-13 level.
"It's a very instilled project and we want to get better every day," Luki Iriarte, La Real's academy director, tells BBC Sport. "We get more information all the time and we are able to focus on the improvement in the youth system.
"Our vision is how we integrate players and how we get the families involved as well, we want a good foundation outside, off the pitch, for us to be able to perform well on it."
Iriarte says the club wants youngsters to "have the chance to be kids first", allowing them to work on different sports before committing to football.
The club does not believe in entering academy tournaments too early and feels their approach allows players to arrive "as open-minded, more flexible individuals".
Real Sociedad's state-of-the-art Zubieta training base, located in the Gipuzkoa countryside 15 minutes outside San Sebastian, is home to both their first team and young players.
Manager Imanol Alguacil is a product of Zubieta, playing more than 100 times in the club's first team, while reserve team boss Xabi Alonso also began his career there.
It worked for the likes of World Cup winners Alonso and Griezmann, who joined Sociedad after failing to find a French club and went on to score 52 times in 201 games before leaving for Atletico Madrid in 2014, while Spain's Alonso starred for Liverpool before trophy-laden spells with Real Madrid and Bayern Munich.
Spain full-back Odriozola is another to join Real Madrid, as did Asier Illarramendi, before returning to San Sebastian. So how do the club stop their best prospects being poached?
"We want every generation to be better than the last," says Iriarte. "This job isn't something that happens at the last moment. The player gets to choose.
"We are very aware we have to take care of our players right from day one, with them being able to see we are committed to the youth system and that our philosophy is based on that.
"We know we are not always going to be able to keep every player who comes through. It is a job we have to do on an everyday basis, to make the players feel they can complete their objectives here at Real Sociedad."
A version of this article was first published on 29 December 2020.
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