These two giants of the modern game have swept all before them with Barcelona. Neymar already has a winners medal from the UEFA Champions League and Super Cup and Messi has four Champions League medals and three for the Super Cup.

But this summer both are set on patriotic challenges that have a deeper imperative even than the traditions of the Catalan club they represent.

Brazil have won the World Cup a record five times - one more than Germany - but they have never lifted the Olympic title. The closest they have come to getting their hands on those gold medals came just four years ago in London, where they were beaten 2-1 in the final by Mexico.

Victory over Spain on home soil in the final of the 2013 FIFA Confederations Cup was the ideal rehearsal for the main event that was to follow in Brazil a year later - but the force was gravely disturbed at the FIFA World Cup finals as the host nation were shockingly defeated 7-1 in the semi-final by a German team en-route to ultimate victory.

As Rio de Janeiro prepares to host the Games of the XXXI Olympiad this summer, a home victory in the national sport is being craved to the point of obsession. Which is why Neymar - who earned an Olympic silver medal in London - will not be taking part in the 100th anniversary tournament of the Copa America - the Copa Centenario - which gets underway in the United States this week.

The Olympic Games is not a protected tournament in the FIFA international calendar so nations cannot demand players’ release.

But the Brazilian Confederation has agreed with Barcelona not to select Neymar for the Copa Centenario. Barcelona, in exchange, will reluctantly release Neymar for the Olympics which is of such importance to Brazil’s players and supporters.

If the passion of the mission requires any further evidence, it lies in the arrangement Brazil have made with their national team coach Dunga, captain of the side which won the 1994 World Cup in the US. For all his status and experience, he has been given to understand that he will only be in charge of the Olympic team if the Copa America campaign goes well.

Representations on behalf of the Brazilian Football Confederation to persuade Barcelona to release Neymar for both the summer competitions have proved fruitless. Barcelona’s President, Josep Maria Bartomeu, has said publicly that it is "certainly not possible" for the 24-year-old to play at both events due to the risk of injury and burnout.

While participation in the oldest continental football tournament in the world is not a top priority for Neymar, such is not the case for his older Barcelona colleague, who is desperate to help deliver a victory that would be as rapturously received in his home country of Argentina as a Brazilian Olympic victory would be in Rio.

Part of the reason for Argentina’s desire to win this year’s Copa America Centenario - the first to be staged outside South America - is historical. For it was Argentina which instigated and hosted the first staging of the competition in 1916.

Argentina wanted to have a tournament to celebrate their 100th anniversary of independence and duly staged the initial tournament in Buenos Aires in a competition that involved the three other existing South American associations of Chile, Uruguay and Brazil. From then on the Copa America was contested annually and then later in different years.

The Copa America Centenario is therefore a celebration of the centenary of the competition and also of CONMEBOL, the South American Football Confederation.

The forthcoming tournament will be the 45th edition of Copa America and it is being held as part of an agreement between CONMEBOL and CONCACAF, the football Confederation for North, Central America and the Caribbean, as a special edition between the usual four-year cycle.

As such it will feature an expanded field of 16 teams, an increase from the usual 12, with all ten teams from CONMEBOL and six teams from CONCACAF.

While Messi’s position does not exactly parallel that of his Barcelona club-mate, as Argentina have won the Copa America 14 times already, only one less than the most successful nation Uruguay, they have not captured this massive trophy since 1993 - when Messi was six.

And in the last two years, Argentina has suffered the frustration of defeat in the finals of both the World Cup, where they lost 1-0 to Germany, and the Copa America, where they were agonisingly beaten 4-1 on penalties by Chile after neither side had managed to score after extra time. That meant five defeats in the last six major finals for Argentina. Needless to say, the one successful Argentinian penalty was taken by Messi.

For all of these reasons, Barcelona’s mesmeric forward will focus on the Copa America rather than representing Argentina at the Rio Olympics, according to national team coach Gerardo Martino.

Messi has already played his part in the Olympics, having been a member of the team as a 21-year-old which earned gold for Argentina at the 2008 Beijing Games.

However, Martino has said he did not think it would be wise to select Messi as one of the country's three over-23 players for Rio 2016.

"Exposing Leo by using him in another competition after all the football he has played would be overkill, in my opinion," said the former Barcelona coach. "It would come back to haunt us in terms of what we have in store in the second half of the year.

"Common sense dictates that he and other players in his position should only feature in the Copa America. Considering the amount of football in their legs, because many of our most important players reach the latter stages of international competitions having played a lot of games, I think it is only logical to take the weight of having to play in both the Copa America and the Olympics off their shoulders.

"I see it as more important for them to be in good shape for World Cup qualifying, for them to be able to spend pre-season with their clubs and have a break after the Copa America."

Messi himself believes his Argentina team deserve to win this uniquely staged edition of the Copa America after losing two major finals in as many years.

“We will try our best to win the Copa, because for us it is very important,” Messi recently told Sports Illustrated. “More so, it has been a very long time since Argentina has won anything, and this group came very close in the World Cup and at the last Copa America. I think we deserve to be champions of an important competition.”

Messi, who has been linked with an eventual move to Major League Soccer when he chooses to leave Barcelona, believes there is no better place for the latest tournament to be held.

“It is a special Copa America, because it is going to be played in the United States - a unique country," he said. "It is the best possible location for the tournament, with amazing stadiums and with a lot of people set to go to the games.”

The US staging of this landmark event might have been disrupted had CONMEBOL not decided that Argentine company Datisa would no longer be involved in distributing sponsorship or broadcasting rights for the tournament.

US investigators froze Datisa accounts as part of a Justice Department investigation into corruption in global football.

A report by ESPN indicated that one of US Soccer's conditions for hosting the tournament was the removal of Datisa - which also had the rights to the 2019 and 2023 stagings - from all portions of the tournament, a process complicated by the fact that some sponsorships and media rights had already been sold, with Coca-Cola and Mexican TV giant Televisa among those already making buys.

But the hurdle for the tournament taking place on American soil was cleared last October when CONMEBOL announced:  "All the sponsorship and broadcast rights related to the Copa America Centenario will be ceded to CONMEBOL effective today.

"CONMEBOL will assume the aforementioned commercial rights while, together with CONCACAF and US Soccer Federation, they are going to identify new partners to commercialise and sell the commercial rights for the tournament using a new and transparent process."

Now the US stage is set, the man who could turn out to be the main player is clear to focus his attention on sporting matters.

“Over the years I have played in the US during friendlies for Argentina and Barcelona but never in a competitive tournament,” he told Sports Illustrated.

“And this one matters for Argentina. We have nearly won our last two tournaments but we came up just short both times. You may be surprised to hear this, but Argentina has not raised a major senior trophy of any kind since 1993, and I think it's important that we end the streak.

“Not that it will be easy, of course. Eight teams in this Copa America Centenario reached the round of 16 at the last World Cup - twice as many as you'll see at Euro 2016 this summer.

“Of course, outside of my family nothing would make me happier than to win my first World Cup with Argentina in 2018. The Copa America this summer is an important step along the way, a chance to show that we can raise a senior trophy for the first time in 23 years.

“And if we can do that, it will also mean spending nearly a month in the US and learning more about this special country. If you Americans are looking forward to seeing me in person, trust me, the feeling is mutual.”

Two of Messi’s colleagues - Napoli strker Gonzalo Higuain and Tottenham winger Erik Lamela - have echoed his sentiments on the eve of competition.

"The Copa America is going to be very difficult," said Higuain, who scored a Serie A-record of 36 goals this season. "But we are going to go out there and try our best to win it, and I will do my best to try and achieve that objective."

Lamela added: "I think the stakes are high because in our last two tournaments we have made two finals, so we've done something right.

"This is a different Copa to the one in Chile but with the same objective Argentina always have, and that is to win the title. The people want a title and we do too."

Argentina's first Copa America clash will be a repeat of last year's final against Chile at Levi's Stadium in Santa Clara, California, on June 6.

After facing Panama in Chicago, Argentina will complete the group stage on June 14 by facing Bolivia in Seattle, one of the country's most passionate soccer markets.

Meanwhile, with Euro 2016 due to start in France on June 10, the US coach Jurgen Klinsmann - whose team will open the Copa America Centenario action on June 3 with a match against Colombia at Santa Clara - has said that the tournament his side will be taking part in this summer might be the better competition.

"If you compare this Copa America with these 16 nations, compared to the 24 going into the Euros, then I almost think you have more quality in this Copa America than you have in this diluted, 24-team version of the European Championship,” said Klinsmann, who was in the German side which won the World Cup in 1990 and the European Championships six years later.

Among the individuals who may help to make Klinsmann’s point in the next month are Brazil’s Willan and Kaka - the latter a late addition to the squad. 

Holders Chile boast a squad which includes Arsenal’s Alexis Sanchez, while Colombia have the flair and scoring power of James Rodriguez to call upon. And while record winners Uruguay will be lacking the predatory talents of Luis Suarez, who has injured a hamstring, they are still expected to mount a formidable challenge.

All eyes, however, are likely to remain upon the slight but incandescently brilliant figure of Lionel Messi.