PARIS • Real Madrid and Barcelona square off in a rare overseas El Clasico, while Manchester United and Manchester City meet for the first time outside Britain as the world's leading football clubs strive to optimise their pre-season preparations.

Pre-season tours have grown significantly in importance over the past decade, as teams promote their brand visibility while simultaneously striving to ensure players are ready to hit the ground running.

Teams like Chelsea, Inter Milan and Bayern Munich are arriving in Singapore this month, with Asia, Australia and the United States being popular destinations for the top clubs, but there is more to these trips than simply pitching up and kicking a ball.

AC Milan and Borussia Dortmund kick off the International Champions Cup (ICC) in Guangzhou, China, on July 18, the first of 19 matches in a pre-season tournament featuring several of Europe's top clubs spread across three countries.

Bundesliga champions Bayern then meet Arsenal in Shanghai before the Gunners take on Premier League title winners Chelsea in Beijing.

"What I really stress (about) whenever somebody comes out here is that the game is probably actually the least important part. It's just 90 minutes," Tom Elsden, senior client manager with Shanghai-based Mailman Group, said.

"You can't expect to come out here on a China tour or do one deal and you've made it. It's a continuous commitment to this market.

"You need to come out every year or other year to continue that connection with fans, relationships with sponsors and grassroots initiatives. It's a long-term play."

The bulk of the pre-season fixtures will take place in the US, where Jose Mourinho's United play Pep Guardiola's City on July 20 in Houston, with European champions Real meeting arch-rivals Barcelona in Miami on July 29 - the first El Clasico held outside Spain since 1982 in Venezuela.

Charlie Stillitano, chairman of Relevent Sports, which oversees the ICC, believes the appeal of the US is its "perfect marriage of commercialism and football".

"It was always thought that pre-seasons should be playing against easy teams, don't stress the players, they will only come to America for marketing purposes," he said. "Now everything has changed. Now the players are serious, the commercial departments are serious."

But Stillitano notes the marked difference between tours to the US and Asia. "The idea of a long pre-season doesn't really exist in China or Singapore," he added. "It's much more commercially driven, they come in, try to play games in a short amount of time, they do their preparation first at home and then leave."

After the Manchester derby, United will play Real in Santa Clara - a fixture that drew a record US crowd of 109,318 at Michigan Stadium in 2014 - before meeting Barca, while City play Real in Los Angeles and round off their tour against Tottenham Hotspur.

"The US, which we're visiting this year, and China, which we toured last summer, are two of the biggest and fastest-growing football markets in the world," says Tom Glick, chief commercial officer at City Football Group.

"There are few better ways to enhance awareness and exposure of our club in particular markets than having our players on the ground, training, playing and meeting fans."

Amy Lawrence, who writes for The Guardian, agrees with Glick, saying that besides the huge amount of money to be made, these tours are probably the best way to connect with fans worldwide.

"The support on a summer tour tends to be made up of members of the international fan base who are ecstatic to have their team actually visit them," she said.

"The tone is brighter, happier, more forgiving compared to the serious business closer to home. The mood brings a refreshing contrast to the routine pressures."

For Arsenal supporter Elia Eliopoulou who lives in Australia, the Gunners' tour of Sydney is a big moment.

"Pre-season tours are not everyone's cup of tea, but they are for the rest of us, the ones who stay up until 3am every weekend for 10 months of the year to follow our club," she said.

AGENCE FRANCE-PRESSE, THE GUARDIAN