Bolivia Match Last Chance for USMNT Back Line to Work on Chemistry Ahead of Copa

There are plenty of concerns surrounding the United States men's national team ahead of the 2016 Copa America Centenario, but the one glaring issue that hasn't had a clear-cut solution yet is the play of the back four. 

It is safe to assume DeAndre Yedlin and Fabian Johnson will start on the defensive flanks throughout the Copa, while John Brooks looks set to occupy one of the two center back positions. However, the final defensive position in the starting 11 has yet to be locked down. 

USMNT boss Jurgen Klinsmann handed D.C. United man Steve Birnbaum a chance to impress on Wednesday in the 1-0 win over Ecuador, but he looked out of place on quite a few plays before Brooks, Michael Bradley and others bailed him out. 

Birnbaum's shocking showing at Toyota Stadium in Frisco, Texas, left the door open for Geoff Cameron and Matt Besler to impress Klinsmann in the final pre-Copa friendly against Bolivia at Children's Mercy Park in Kansas City. 

Cameron would be the logical option to play next to Brooks. The Stoke City man, who missed Wednesday's match with an injury, brings the calming influence of a veteran when he plays next to the youthful Brooks on the international level.

Cameron has also grown into a leadership role over the last year with the Yanks. That quality should not be underestimated in a pressure-packed tournament on home soil like the Copa. 

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The best news Cameron could've received ahead of the tournament had nothing to do with him directly, as each of the other positions he could play were filled by consistent starters. Yedlin is the right-back of the present and the future, while Michael Bradley looks best in red, white and blue in the No. 6 role. Even if Klinsmann opts to use Bradley in an advanced role, he has Jermaine Jones and Kyle Beckerman to start in the defensive-midfield position. 

In the past, Cameron has been the Swiss army knife of the USMNT due to his versatility, but his best position on the international stage is center back. There is no way Klinsmann will experiment with two young center backs for the second consecutive summer, which means Birnbaum should be relegated to a bench role. 

The only wild card in this situation is Besler; Klinsmann may give him a runout in front of his home crowd in Kansas City on Saturday night. Klinsmann could opt not to risk Cameron and play Besler from the start or split 45-minute shifts between the pair.

Regardless of who starts on Saturday, and for the rest of the Copa, that player must have a good positional understanding with Brooks. There were too many occasions on Wednesday when Birnbaum and Brooks looked disjointed and allowed Ecuador to exploit the space in the middle of the pitch. 

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If any center back allows an opposing side to have that much open field during the Copa, the USMNT will be doomed. The expectation with Cameron and Besler is they will be able to build up chemistry with Brooks to form a quality back four alongside a pair of full-backs who could be difference-makers during the June competition. 

Yedlin has made it clear in the last two USMNT friendlies that he is a changed player on the defensive side of the pitch. Sam Allardyce worked wonders with the 22-year-old at Sunderland this season, and the USMNT are already starting to reap the rewards of Yedlin's development. Yedlin received a good warm-up for the Copa on Wednesday against Jefferson Montero, as the Ecuadorian charged at him quite a few times in the first half. 

The Yanks should receive plenty of quality out of Johnson, but it may take a few matches for the Borussia Monchengladbach player to become a massive contributor on both ends of the field.

It's worth noting the 28-year-old spent the entire Bundesliga season at left wing. Johnson is a good enough player to adjust to left-back right away without too many kinks, but he may not surge forward as much due to his defensive responsibilities. 

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As long as the center backs and Bradley provide cover for the full-backs when they bomb forward, the Yanks should be set to attack opponents from all angles.

If Yedlin and Johnson are at their best on Saturday, and at the Copa, the USMNT could play one of the most attractive brands of soccer at the tournament. However, if opposing wingers occupy too much of their time or the full-backs choose the wrong time to move up on the pitch, the Yanks will be in for a long month.

How the defensive unit works together as a whole will be under the microscope on Saturday, just like every other aspect of this squad as it carries a massive amount of pressure into the Copa after the shortcomings of the 2015 CONCACAF Gold Cup.

If the back four displays signs of cohesion with either Cameron or Besler at center back, the Yanks will enter the June 3 opener against Colombia with plenty of confidence. 

Joe Tansey covers U.S. Soccer for Bleacher Report. You can follow him on Twitter, @JTansey90.