GLENDALE, Arizona—As the United States national team prepares to take part in its next chapter against arch-rivals Mexico, much of the focus has been on the team’s offense. That’s understandable give the reunion of Landon Donovan, Michael Bradley, and Clint Dempsey, and the addition of Julian Green.

The truth, however, is that the team’s backline will be under pressure. This group will dictate the American's success at the World Cup in Brazil against powerful opponents Ghana, Portugal, and Germany. Unlike the team’s offensive core, the defensive unit offers more questions than answers with kickoff less than 80 days away.

Three-time U.S. World Cup goalkeeper Tony Meola likes what he sees in the national team, but he has concerns about the back line. Meola is in Arizona today and will be appearing in the Allstate Fan Zone, chatting with fans before the match.

"The front six, I think we're going to succeed at," he told ASN. "Obviously, in goal we're very strong. The question mark is in the back. I don't know that we've gone into a World Cup—and I've been involved with all of them whether it was a player or a fan—where we were this unsure about our back four."

"I'm sure we can compete, but we still don't know who our back four are. I'm convinced that Jurgen and his staff—his new staff—will get it right, but I can't really remember a time when we were three months away from the Cup and we didn't know three of the four [starters]. For so many years we could just write [the names of the defenders] in. If anything, we had questions about the other positions."

In central defense, the first choice remains uncertain. There is the obvious question as to whether or not Geoff Cameron will remain at right back or shift into the middle. Assuming he stays out wide, the three likely candidates to start in Brazil are Matt Besler, Omar Gonzalez, and Clarence Goodson who are all now based in MLS and in camp in Phoenix.

While Clarence Goodson’s tenure on the U.S. team predates Jurgen Klinsmann’s arrival in 2011, the addition of Omar Gonzalez and Matt Besler into the core team has been a project for the German coach. The smooth passing, left-footed Besler knows that tonight’s game against Mexico is crucial to establishing chemistry since it is the final friendly before the opening of World Cup camp in May.

“I think that we’re comfortable with each other, whoever is back there,” said Besler. “But I think we all understand that there is still work to be done. It is camps like these where you try to take advantage of that. Any training session we get, we’re extremely focused to work together. Any game we get we’re focused on getting results because there’s not a lot of time before Brazil.”

Goodson, 31, is by far the most experienced of the central defenders in the player pool and is older than Besler, 27, or Gonzalez, 25. At times it appeared that Goodson was the preferred choice to start with Besler given that at the Gold Cup last year, Goodson started the final over Gonzalez. At the conclusion of the recent month-long January camp, however, Besler and Gonzalez started ahead of Goodson in the 2-0 win over South Korea.

It has consistently been a challenge for Goodson to establish a role within the U.S. team. He was one of the few players on the roster who did not see any minutes at the last World Cup. Still, he is confident in the resume he has put forth singling out his strong effort in last September’s 2-0 win over Mexico in Columbus to clinch a berth in the World Cup.

“I go out there and do the best I can every time,” Goodson explained. “I try to be a good professional and be a good player in practice and hopefully that translates into the games—hopefully starting. But you never know what is going to happen. I think I’ve proven in the past that when I’ve been given the opportunity, I’m capable of doing the job. I’ll just continue along that same mind-frame and hopefully the starts and making the teams will follow.”

For Gonzalez, his finest moments for the national team have come against Mexico in 2013 when he started both the 2-0 win in Columbus with Goodson and in the 0-0 draw at Azteca while partnered with Besler. The Los Angeles Galaxy defender with Mexican heritage now has his sights set on a third consecutive shutout in the rivalry regardless of who he plays with or if he plays. Either way, the team’s intensity is at a high level these days.

“Right when we got into January camp, the intensity has gotten to be a little tougher and it’s all going to get even tougher now,” Gonzalez said. “The expectations are only going to get higher. But that’s to be expected.”

“Nothing really changes when I play with Matt or Clarence," he added. “They’re both easy to play with. They’re both very good players. I enjoy playing with both.”

While the central defense questions are still lingering for Klinsmann, the full back positions are also even more perplexing. A safe bet would suggest that against Ghana, Stoke City’s Geoff Cameron would start at right back and Hoffenheim’s Fabian Johnson would start at left back. Both players are competing at a high level week in and week out, but there is a chance that Cameron could shift centrally or Johnson could play in the midfield since Klinsmann has preferred those positions.

If that happens, what are the options? Tonight’s game against Mexico will provide an opening to other players since potential starting right back Brad Evans (injured) and left back DaMarcus Beasley (not released) are not in Phoenix.

So the door is now open for others to claim a spot in the cycle’s final weeks. Seattle Sounder’s 20 year old DeAndre Yedlin is coming off an exceptional rookie season but is untested at the international level with just one late cameo against South Korea in February. Still, the personal changes within the team could open the door for him since late addition Tony Beltran is the only other right back.

Besler, for one, is excited for Yedlin’s future on the team.

“A ton of potential, a ton of talent,” he said of the youngster. “He has a lot of intangibles that a lot players don’t have. He would be a player to get excited for.”

Yedlin knows the opportunity that awaits him and that circumstances this week have opened the door for him perhaps more than expected. He is used to the big game environment that playing in Seattle offers and feels optimistic he can rise to the challenge.

"If that opportunity comes, of course it’d be an amazing opportunity,” Yedlin said. “I’m definitely up for the challenge and I’m looking forward to it."

No matter the result, Wednesday will be a learning experience for Jurgen Klinsmann as to where his backline stands heading into the May camp. The benefit of playing a rival like Mexico is that the game will provide the closest level of intensity to the World Cup that a friendly could provide.

Goodson has been on both sides of the heating nature of games against Mexico. He has presided over wins against El Tri that have clinched World Cup qualifying as well as a 5-0 loss in the finals of the 2009 Gold Cup in New Jersey. There is always something at stake in these games and Goodson is eager to take part in another chapter.

“We’re always excited to play against Mexico, that’s our biggest rival,” Goodson said. “It’s not a game where you need to fire people up and get people motivated. This is one that really speaks for itself. Guys know what it’s all about, especially the ones who have been around it before – a lot of bragging rights and everything else. It’s all been said at this point, but this is a big one. It’s always hard fought and it’s always intense.”

What's your biggest concern about the backline? Who should start in Brazil? Give us your take below.

Brian Sciaretta is an American Soccer Now columnist and an ASN 100 panelist. Follow him on Twitter.