Defeat to Honduras last month in the opening game of the six-team final qualifying stage from the North and Central American and Caribbean region, set alarm bells ringing for the U.S who have not missed a World Cup finals since 1986.
A host of injuries, with eight likely squad members ruled out for Friday's game and the fixture in Mexico City four days later, added to the nervousness of many American fans, and means Klinsmann will be forced to play with a very inexperienced back-four and reserve keeper Brad Guzan.
The German is also understood to be seething about a report, published as the team gathered in Denver, in which unnamed players and other anonymous figures in the game criticised his approach and tactical nous.
It is rare controversy for a U.S team which in recent years has been a model of dressing room harmony and professionalism and which has avoided the kind of media criticism common in countries with a traditional passion for the game.
But, as they showed frequently under Klinsmann's predecessor Bob Bradley, the Americans tend to produce their best when facing adversity and if the words of the players are any guide at all, the mood in the camp is firmly defiant.
Bradley's son Michael, the heart of the U.S midfield, lambasted Klinsmann's unknown critics as "shameful" and "embarrassing" for speaking outside of the locker-room and said despite the absentees, the U.S need to show their character and get the win they need.
"We have to do that. That's the challenge. When you look back, this team has always had to deal with injuries, suspensions," he told reporters.
"We have faith in every single guy. There is a commitment and a pride and a determination from every guy who puts on this shirt. It's our job to make sure that on the biggest nights and most important of games, it shines through."
Tottenham Hotspur forward Clint Dempsey, named captain for the upcoming games, shrugged off the controversy and said it was far from the players' minds.
"The thing that matters is getting three points, winning the game and qualifying for the World Cup... it doesn't matter about the little petty things here and there. We're focused," he said.
The focus will be particularly needed in defence where Stoke City's Geoff Cameron suddenly finds himself the most experienced player - with six appearances in qualifiers.
German-born full-backs Timmy Chandler and Fabian Johnson are both out with injury and Carlos Bocanegra, with 110 caps to his name, isn't playing at club level, in the Spanish second division, and has been left out.
Klinsmann will have to find the right mix because Costa Rica, who drew with Panama in their opening game of the 'hexagonal' phase, possess a potent attacking trio in Bryan Ruiz, Alvaro Saborio and Joel Campbell.
The German has called the game a "must win" and certainly the U.S would not want to be heading to the Azteca, where they have never beaten Mexico in a competitive game, without points on the board.
"Every home game in the hexagonal is a must-win situation. You want to get all the points possible in your home games so, independent of the result in Honduras, it's a must-win on Friday
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