This shy 18-year-old forward is the player whom Diego Maradona himself hails as his true successor and the one every Argentinian wants to see spearhead their bid to win the next World Cup. The only problem for Barcelona, and as a consequence for Argentina, is that a bureaucratic oversight could end up depriving them of the services of their prodigy for much of this season's league matches. Although he came to Barcelona five years ago, the club have not done the paperwork that would have allowed him dual citizenship and to become eligible to play for the first team.
Under Spanish Football Federation rules each Primera Liga club is allowed a maximum of three non-European Union players in their squad and Barça have already filled their quota with Ronaldinho, the leading striker Samuel Eto'o and the Mexican international defender Rafael Marquez.
They had been hoping that Messi would not count as a "foreigner" because he had come up through the club's youth ranks and could therefore be seen as an "assimilated" player, but the lack of a definitive ruling over his status has forced them to leave their most prized possession on the sidelines in the league.
Fortunately for Barcelona the same rules do not apply in Europe and Messi is able to play in the Champions' League. In fact, he came on in the second half of their game away to Werder Bremen on Wednesday to win the penalty that sealed a 2-0 victory for the Catalans.
"I'm managing to cope with the situation quite well, but I just hope it is all sorted out soon," the youngster said after the match.
So how good is Messi? Born in the city of Santa Fe, Leo started out in the youth teams at Newell's Old Boys, but his football career came under threat almost before it had started because a hormone imbalance threatened to inhibit his growth. No Argentinian club was prepared to finance the expensive treatment, so his father Jorge decided to take him to Spain to try his luck with Barcelona. It took just a few touches of the ball for Messi to convince the then Barça coach, Carlos Rexach.
"I signed him up in half a minute and we signed a symbolic first contract on the back of a napkin," he said. "I knew immediately that he had everything needed to be a footballing superstar." His 31 goals in 38 games for the Barça junior teams brought Messi to the notice of the coach, Frank Rijkaard, who made him the third youngest player ever to play for the senior side when he gave him his debut in a friendly against Porto in November 2003 at the age of 16.
Last term he made his European debut in the Champions' League against Shakhtar Donetsk and played his first league match against city rivals Espanyol in October. He became the youngest player ever to score for the first team with a last-minute lob in the 2-0 win against Albacete.
In June, Messi steered Argentina to a record fifth triumph in the World Youth Championship in the Netherlands. He converted two penalties to lead his side to a 2-1 victory over Nigeria in the final and, like Maradona before him, he ended the tournament by pocketing both the top scorer and best player awards.
"He's a genius," Maradona said after the victory. "He's a leader who is not weighed down by responsibility and without him this Argentinian team would have no football."
Messi received a call-up for the full national squad for a friendly away to Hungary in August, the same opponents against whom Maradona made his international debut at 16. What should have been a dream turned to a nightmare, though, when Messi was sent off less than a minute after stepping on to the pitch as a substitute as the referee Markus Merk adjudged he had elbowed a defender who had pulled his shirt as he surged through the Hungarian defence.
When the team returned to the dressing-room after the 2-1 victory they found the youngster crying in a corner. The Chelsea striker Hernan Crespo said that even though Messi's debut had been cut short his team-mates knew they were in the presence of a special player. "When Messi came on we were all aware that something had changed and a magical player had come on to the pitch," he said.
Barça fans pray that the club can sort out the paperwork so that one of the most exciting prospects in world football does not end up spending most of the season sitting in the stands.