Charly Rexach grins a familiar grin. “I’ll go down in Barcelona’s history,” he says. Born and raised in Pedralbes, the smart neighbourhood that lies up the hill from the Camp Nou, Rexach joined Barcelona at the age of 12 and he has spent almost half a century there, on and off. He played for the first team for 17 years and has been coach, assistant coach, technical director and presidential adviser. But that’s not why he says he will go down in history. No, Rexach says he will go down in Barcelona’s history because one day he signed Lionel Messi – on a serviette. Or so the story goes.

Horacio Gaggioli still has the serviette hidden away somewhere, although there have been calls to place it in Barcelona’s museum. Every now and then he takes it out and shows it off carefully. On Sunday, 17 September 2000, Gaggioli was waiting for Messi at El Prat airport in Barcelona. Messi, aged 13, was flying across the Atlantic with his father, Jorge, and Fabián Soldini, the player’s agent and Gaggioli’s partner. Together with Josep Maria Minguella, they had arranged for Messi to have a trial at Barcelona.

Minguella had told Rexach, Barcelona’s technical director, that this kid was like Diego Maradona. Minguella knew: he was the one who had brought Maradona to Barcelona 20 years earlier. They put Messi up in the Hotel Plaza, at the foot of Montjuïc, where escalators head up the hill to the Olympic stadium. The following day, Messi trained with the Barcelona youth team, Cesc Fàbregas and Gerard Piqué among them. Messi did not reach five feet and he changed in silence. In the dressing room, they looked at him and could not believe how small he was; on the pitch, they looked at him and couldn’t believe how good he was.

That day, Rexach was at the Olympic Games in Sydney. Messi impressed and he stayed until Rexach returned. A game was arranged for the start of October so that the technical secretary could be there. Rexach was late; Rexach is always late. He arrived with the game under way and strolled round the pitch to take up his place, first behind the goal and then on one of the benches. It took him seven or eight minutes to get round and by the time he arrived, his mind was made up: “We have to sign this kid right now.” “After two minutes, I knew,” Rexach says. Then he adds: “Anyone would have said the same.”

Rexach starts to explain how Messi came to find the perfect environment at Barcelona; how it all seems so natural these days. But back then, it was not so simple. Joan Gaspart had become president that summer, Luís Figo had left for Real Madrid, and Barcelona were in crisis. And as for Messi, he was special, sure, a player they thought would make it to the first team. But in 2000, you didn’t just sign a 13-year-old and certainly not a 13-year-old from Argentina.

They had to find work for his father. They had to pay for the hormone treatment that, painfully, Messi injected into his legs every day. That was not cheap at almost $1,000 a month. And the £40,000 they agreed to pay Jorge Messi annually was a lot of money; some thought it too much for a player so young about whom there could be no guarantees. A foreigner, Messi could not play with the Juvenil A team and was initially able to play only in Catalan competition. In the dressing room, they often referred to him as el mudo, the mute one.

Messi moved into the Hotel Rallye and from there to a flat on the Gran Vía de Carlos III with his family. From the windows of the Rallye, you can see the Camp Nou barely 50 yards away. But it was no foregone conclusion that Messi would get there; certainly not for Barça. As he played, his father waited and waited. The original agreement had been laid down early but nothing had actually happened. Other clubs were interested, Messi’s agents warned, clubs such as Real Madrid.

“His dad was getting angry and said Leo was leaving,” Rexach later told the sports daily AS. On 14 December 2000, he met for lunch with Minguella and Gaggioli at the Pompeia tennis club. “We’ll go elsewhere,” Gaggioli told him. Rexach pulled out a serviette from the little plastic holder and started scribbling: “I, Charly Rexach, in my capacity as technical secretary for FC Barcelona, and despite the existence of some opinions against it, commit to signing Lionel Messi as long as the conditions agreed are met.”

The framed napkin on which Lionel Messi’s informal Barcelona contract was written by Charly Rexach in December 2000. Photograph: Manu Fernandez/AP

The line that stands out is “opinions against it”; the line that reveals that some at the club were not convinced. There had been arguments at boardroom level. The first team were struggling and Gaspart was under pressure, tumbling head-first into an abyss. Soon, the Camp Nou would be full of fans waving white hankies and chanting for him to resign. Barcelona were about to embark upon a five season trophyless run, their longest since the 1930s. They would not win anything until 2004-05, by which time Gaspart had gone, they had a new president and Messi was in the first team.

For now, he was a long way from the first team and a kid from Argentina was not the priority. But that very night the club’s director general laid out the agreement again – officially this time, on proper paper this time. And, as Gaspart insists, irritated at the popular and unfair image of him as an obstacle to Messi joining, the club he presided over did finally commit to signing the player who a decade later this week stands on the verge of becoming the all-time leading scorer in La Liga, aged only 27.

All was not yet resolved. As Graham Hunter reveals in his superb book on Barcelona, six months later Jorge Messi wrote to the club president because he had not been paid and the family situation was, he said, “very serious”. Messi’s official international transfer wouldn’t arrive until August. And that summer, Messi’s mother and three siblings returned to Argentina. Leo was asked if he wanted to join them. He insisted on staying. He was determined to make it. In December 2001 he signed a new contract.

Things were moving. Messi was progressing quickly, racing through the system, scoring goals. Cadete, Juvenil A, Juvenil B, Barcelona C, Barcelona B and then the first team. As he accelerated, he went through five levels in barely a year and a half. In November 2003, Barcelona went to Porto for a friendly, the inaugural game in the new Estádio do Dragão. Frank Rijkaard asked for some kids to fill out the team and Messi was one of them. “He is a boy with a lot of talent,” Rijkaard said.

His competitive debut came on 16 October 2004, a decade agotomorrow, against Espanyol at Montjuïc, a stroll up the escalators from the Plaza de España where Messi spent his first night in Barcelona. He replaced Deco in the 82nd minute of a game that one headline paper described as “not much of a derby”. Asked about the shirt he wore, he replied: “That’s for my mum, who is back in Argentina,” adding: “I will remember those 10 minutes my whole life.”

Others would not, until now. A brief article at the foot of page five of the Catalan sports newspaper El Mundo Deportivo noted that he was the youngest Barcelona player since Paulino Alcántara made his debut in 1912 and that was pretty much that. Beside his name on the paper’s team sheet, it said “sc”, sin clasificación: he had not been on long enough to even get a match rating. “He hardly had time to shine,” it said. Leo Messi had not done much. Not something that could be said often over the next 10 years.