Germany, who take on Ghana, Portugal and United States in Group G, leave for Brazil on Saturday evening with 22-year-old Sampdoria defender Shkodran Mustafi booking an unexpected last-minute ticket following Reus's injury.
Reus turned his ankle shortly before the break in their 6-1 victory over Armenia on Friday in Mainz, partially tearing the anterior ligament above his left ankle on the eve of the team's departure for Brazil.
"Both for him and for us it is extremely bitter," coach Joachim Loew told reporters. "Marco was in top form and both in the training camp and in the friendlies against Cameroon and Armenia left an outstanding impression.
"He had played a central role in our planning for Brazil," he said.
The lightning-quick Reus, who enjoyed a superb season at Borussia Dortmund, was seen as a key player in Germany's quest to claim their first international title in 18 years.
Mustafi, who won his only cap in May against Poland, was surprisingly part of the provisional squad but missed the cut as one of three players omitted from the final squad earlier this week.
"It was not about replacing Marco Reus in the same position," Loew added. "We have a lot of quality in that position and a lot of options with Lukas Podolski, Andre Schuerrle, Mario Goetze, Thomas Mueller, Mesut Ozil, Julian Draxler and Toni Kroos,” he said.
"That is why we decided for an option in defence and Shkodran had been convincing in our training camp, he is fit and we have full confidence in him," he added.

Germany eager to end World Cup third-place curse

Germany head to Brazil aiming to end their 24-year wait for a fourth World Cup title with captain Philipp Lahm insisting he is sick of finishing third.

Consecutive semi-final defeats have led to Germany taking bronze at both of the last two World Cups with Lahm in the side and it is 12 years since the Germans lost the 2002 final to Brazil in Yokohama, Japan.
"I do not want to go out in the semi-finals again or visit Brazil just to soak up the sun," insisted Lahm after a decade in the Germany team.
"I have a clear goal, to achieve the biggest possible success and win the World Cup."
In order to break their duck, improved counter-attack and a tighter defence are the key areas coach Joachim Loew wants to improve.
The squad is packed with attacking potential, but there have been rumours of discontent in the past with disgruntled stars disrupting the squad's harmony from the bench at both the 2012 European Championships and in the World Cup qualifiers.
"We have the necessary punch to win the title, but we must be sure that the talent and ego of every individual provides only for the team's benefit," said Lahm with team building also a priority in their south Tirol camp.
The 24-year wait for a fourth World Cup title is Germany's longest since first winning the global crown in 1954.
Younger members of the squad, including midfield star Mario Goetze, were yet to be born when West Germany won Italia 1990 -- the last time they were world champions.
In the past, Loew's strength has been to instill impressive cohesion into his side by hours of drilling. But injuries and a lack of fitness in his first-choice stars could hamper the process.
"We need to work on our flexibility and variation," said the 54-year-old.
"You always need a 'what-if' strategy during matches, but we also need to improve our counter-attacking when we have won the ball back.
"We haven't done that as consistently well as we did at the South African World Cup and immediately after."
In 2006, captain Michael Ballack was nursing a calf injury while current skipper Lahm needed elbow surgery.
In 2010, Chelsea's Ballack was ruled out by a nasty tackle in the FA Cup final from Ghana midfielder Kevin-Prince Boateng while first-choice goalkeeper Rene Adler was ruled out with broken ribs.
In Ballack's absence, Lahm took over and has been Germany's captain ever since while Manuel Neuer has cemented his place between the posts and is widely regarded as one of the world's best goalkeeper.
However, four years on and the fault line runs right along the back-bone of Loew's first-choice side.
Lars Bender's withdrawal has removed a defensive midfield option with Loew's first-choice pairing of vice-captain Bastian Schweinsteiger and Sami Khedira both lacking fitness after respective knee injuries.
Likewise, Neuer is battling a shoulder injury – never good for a goalkeeper -- while Lahm is also being treated intensively for an ankle knock.
Loew does not have the luxury of a settled back four and is also low on options up front with only two recognized strikers in his squad.
Miroslav Klose, who turns 36 next month, has missed large chunks of the season with Lazio, and Hoffenheim's 21-year-old Kevin Volland is inexperienced, but Loew could also convert one of his midfield stars into a 'False Nine'.
'Germany feeling pressure'
Traditionally, Germany have boasted strong leaders -- characters such as Stefan Effenberg, Michael Ballack or Oliver Kahn.
But both Lahm and Schweinsteiger have been criticised for their lack of leadership when things go wrong -- namely in the Euro 2012 semi-final defeat to Italy and the 2010 World Cup defeat to Spain for a place in the final.
"Germany have a superior team - and that's the problem," according to Ghana midfielder Boateng.
"Germany are feeling the pressure to be world champions, but they don't have the characters and types of player to deal with that in Brazil, someone like an Effenberg or a Ballack,” he said.
"When the pressure comes on, they (Germany) don't pull through," he added.
In the pressure-cooker cauldron of the opening Group G match against Portugal on June 16, Loew will discover what is young side is made of.


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