In late summer 2008, 20-year-old Sergio Busquets was a reserve in Barcelona’s B team. Luis Enrique, the coach, saw no role for the slow, gangling midfielder who lumbered around like a mal-coordinated giraffe. It fell to Pep Guardiola, Barcelona’s new head coach, to save Busquets’ career.

Guardiola had previously trained “Busi” in the B team and knew from his personal experience as a slow midfield player that a suboptimal body sometimes camouflages a brilliant footballer. That September, Busquets made his debut for Barça’s first team in a dispiriting home draw with Racing Santander. Within 22 months, he had won football’s biggest club prizes, and the 2010 World Cup.

When Spain meet Italy in the semi-final at Wembley on Tuesday, they will be coached by that very same Luis Enrique and captained by Busquets, gunning for his second European title, the last survivor of the Spanish world champions, Spain’s indispensable player.

Busquets’ father, Carles, was an unreliable goalkeeper with Barça in the 1990s, good with his feet but less so with his hands. Busi grew up playing in his tough working-class suburb of the city, until Barça finally took him aged 16.

Slow players learn to think fast and the “pivote” was a rare footballer who was as good without the ball as with it. Barcelona’s data analysts did not dream of giving Busi advice. Instead, they studied his decisions to understand how football works.

Behind every Busquets pass is a thought: either he splits the opposition’s lines or passes side to side to disorganise their structure. His trademark head fake throws off pressing opponents. He moves his team slowly forward in compact formation, pass by pass, forever repositioning himself to be the apex of the next passing triangle.

At the same time he organises his team’s pressing, foreseeing where loose balls will fall. An unobtrusive genius, he makes football look simple because he is always in the right place, facing the right way. He also knows when to foul.

“He is logical and streetwise, an almost unbeatable mix,” noted Spanish football writer Santiago Segurola. “He has all the moral weaknesses that help in football,” observed Arsène Wenger, Arsenal’s longtime manager.

Success has not changed him. Busquets has stuck with his mates from his old neighbourhood, ignores social media, speaks out only when his obsessive tactical thinking impels him to, and seeks no plaudits, which he seldom gets anyway. A dark, brooding, aggressive and unsmiling player, who rarely scores or assists or even passes more than 10 metres, he has never become a fan idol.

But his peers revere him. Steven Gerrard, the former Liverpool midfield player, once described the “absolute nightmare” of playing against him: “In the end you stop pressing him because it’s so frustrating. You can’t get the ball off him, you can’t get close. If you come out of your position to press him, he pops it around you — and you can’t do it for 90 minutes because you’re just using useless energy up.”

Above all, Busquets is a coach’s footballer. “If I was reincarnated as a player, I’d like to be like him,” said Guardiola. “A player from an extinct species,” Cesar Luis Menotti, the former Argentina manager, once marvelled.

Shortly before the tournament Busquets was carted off into isolation in an ambulance and diagnosed with Covid-19. Spain’s captain, now nearly 33, knew it could be weeks before he tested negative and feared missing his last European championship. Enrique decided there would be no replacement. “I will wait for Busi,” he said.

Without Busquets, a sterile Spain drew their first two matches, unable to move the ball forward. On his return, “La Roja” thrashed Slovakia 5-0 and Busquets was named man of the match. For his mostly inexperienced teammates, the most reassuring sight in football was “Busi” bossing midfield. “I’m emotional,” he said in his post-match interview, through very uncharacteristic tears. “I didn’t know if I could come back or not, but the group is strong . . . ” and then he couldn’t speak any more.

He was man of the match again against Croatia. Against Switzerland he controlled the tempo, but missed a penalty in the shootout. Against Italy, he should surpass Toni Kroos of Germany to become the footballer with most completed passes in major tournaments since 2010.

But terrifyingly for La Roja, Italy are arguably a more authentic version of Spain’s true self. Busquets’ description of Spain’s style — “to dominate the game, have the ball, recover it as quickly as possible, press like a real team” — applies word for word to Italy. And only one side can dominate.

If it’s Italy, they will plunge Busquets into his zone of discomfort: wide open space. “Busi” is the master of the square metre. In the phrase of Johan Cruyff, the spiritual father of Barcelona’s football, a walking brain like Busquets can defend a single table, but if he has to defend a whole restaurant, he is lost. In recent seasons, when Liverpool and Bayern Munich made Barça play across an entire field, they extinguished Busquets and won 4-0 and 8-2 respectively. The Azzurri, unbeaten in 32 games, will aim to stretch Wembley into a restaurant.