Why are Barcelona and Manchester City playing a friendly at Camp Nou three weeks into the season?

Guardiola: Haaland has a lot of margin to improve (0:49)

Pep Guardiola feels Erling Haaland has plenty of room to get even better in his time at Manchester City. (0:49)

Pep Guardiola returns to Camp Nou on Wednesday as his Premier League champions Manchester City take on LaLiga giants Barcelona in a friendly match, despite both clubs having kicked off their 2022-23 seasons weeks ago.

City are three matches into the title defence they began on Aug. 7, having lost to Liverpool at Wembley in the Community Shield eight days previously on July 30, while Barca will play their third game of the season on Sunday against Real Valladolid (stream LIVE at 1:30 p.m. ET on ESPN+ in the U.S.). And before that, both clubs travelled to the United States for their preseason tours, racking up six games between them across the Atlantic last month.

But they have still found time in their schedules to play in Wednesday's match, which is for a worthy cause that is close to Guardiola's heart as well as all those involved with Barca.

A lot has changed since City last played at Barcelona, where Guardiola won two Champions Leagues among 14 trophies during his glorious four years in charge from 2008-2012. On that occasion, in 2016, Lionel Messi struck a hat trick and Neymar added a late fourth after City goalkeeper Claudio Bravo was sent off early in the second half in a Champions League group-stage game.

The clubs' trajectories have gone in opposite directions since then. City have got better and better under former Barca coach Guardiola, winning the Premier League in four of the past five seasons, although European success still eludes them.

Barca, meanwhile, have lost Messi and Neymar, racked up more than €1 billion in debt and fallen away from Europe's top tier of clubs, winning just one Copa del Rey during the past three seasons. There is hope, though, after a summer of more spending, that they're ready to reassert themselves as one of the continent's best sides -- especially under coach Xavi Hernandez, Guardiola's protege, who will be facing his mentor in the dugout for the first time.

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Why are Barcelona and Man City playing this match?

This friendly was originally scheduled to take place last year, but it was postponed due to the coronavirus pandemic. The attendance would have been capped at 30,000, per local government restrictions at the time, and the clubs wanted the game to be played in a full stadium -- Camp Nou holds almost 100,000.

That's because the money raised from the game will go towards research into amyotrophic lateral sclerosis (ALS) in the name of Juan Carlos Unzue, who was diagnosed with the condition at the start of 2020.

Barca and City had looked for a date in preseason, but summer tours abroad took precedence and it proved impossible to find a day that worked for both teams. Therefore, they reached the slightly unusual decision to hold the match this Wednesday, even though both sides have already started their domestic seasons.

Who is Juan Carlos Unzue?

Unzue is a goalkeeper-turned-coach who spent most of his career at Sevilla. He also has strong links with Barcelona, where he was the club's backup goalkeeper between 1988 and 1990, although it is as a coach that he is most renowned at Camp Nou. He became the goalkeeping coach for Frank Rijkaard's Barca upon retirement and maintained that position under Guardiola.

He later tried his luck as manager at Numancia and Racing Santander before becoming Luis Enrique's assistant at Celta Vigo in 2013. He followed Luis Enrique to Barca a year later, where they went on to win the Treble in 2015.

Following spells in charge of Celta and Girona, he was diagnosed with ALS in 2020, which is the most common form of motor neurone disease.

Unzue, rarely seen without a smile and now in a wheelchair, has been raising money to fund ALS research, and Barca wanted to play a role in that fundraising. City, coached by Unzue's friend Guardiola, were an obvious opponent and also a glamorous one in terms of generating interest.

Why are Barcelona the only club to regularly play friendlies during the season?

Barca have developed a habit of playing friendlies at awkward times, although it is usually to benefit their own coffers rather than to raise money for charity.

They ended last season with a trip to Australia to play an A-League All-Stars team in Sydney. That fixture was reportedly worth €5 million to the Catalan club.

In December 2021, they travelled to Saudi Arabia to face Napoli in the Diego Maradona Cup, after the death of the Argentine forward the previous year. Two clubs where he spent more time than Barca, Argentinos Juniors and Boca Juniors, did not get an invite. It was another money spinner for the Catalan club.

In 2018, just before the end of the season, Barca also organised a trip to South Africa to play Mamelodi Sundowns. Many still blame that fixture for costing Ernesto Valverde's side an unbeaten season. Just three days earlier, they lost their penultimate game of the season, which was their only defeat in that campaign, 5-4 to Levante. The coming trip and contract stipulations about certain players having to play in South Africa was said to have been a distraction.

Barca also host the Joan Gamper Trophy annually at Camp Nou, although that fixture comes the week before the start of the new campaign. Pumas UNAM, Juventus, Elche, Arsenal, Boca Juniors and Chapecoense are recent guests.

Will this impact the teams' starts to the season?

Barca have a bloated squad so Xavi may view this game favourably. It represents a chance to give more minutes to new signings Franck Kessie and Raphinha, who were both substitutes in the weekend win at Real Sociedad, and Jules Kounde, who is not yet registered to play in LaLiga due to the spending cap imposed by the league.

Xavi may also take the chance to give some playing time to Gerard Pique, Sergi Roberto, Miralem Pjanic and other players who have not featured regularly in the two LaLiga games played thus far.

The fact it is played at Camp Nou is also a positive, as it means no midweek travelling ahead of Real Valladolid's visit on Sunday.

Guardiola may not have such a positive view on proceedings. City had an inexperienced bench as they were held 3-3 by Newcastle United on Sunday, although they were still able to leave out players of the ilk of Riyad Mahrez and summer signing Kalvin Phillips.

Like Xavi, then, Guardiola is likely to take advantage of this fixture to get a better look at Phillips, Julian Alvarez and new signing Sergio Gomez, a Barcelona academy product.

Speaking at the presentation of the game back in June, Guardiola said he would field a strong side and City arrived in Girona, just north of Barcelona, with all of their star players on Sunday.

A lot of focus will fall on City midfielder Bernardo Silva. Barca have made no secret of their desire to sign the player -- president Joan Laporta even made a joke of it at that presentation in June -- but he will be wearing City blue on Wednesday. Despite the Portugal international telling ESPN's Rob Dawson earlier this month that his future is uncertain, City say he is not likely to leave in the summer transfer window and Barca's financial position suggests they may not even be able to test City's stance.