How deep, prepared is the U.S.?

What's more, considering this week's foes are the two bottom-feeders in the CONCACAF Hexagonal -- El Salvador (8 p.m. ET, Saturday, ESPN Classic) and Trinidad and Tobago (7 p.m. ET, Sept. 9, ESPN Classic) -- six points are certainly desirable for the Americans, four points would be disappointing and anything less than four would be cause for major alarm.

This is the week that we'll learn how deep this U.S. roster really is. For starters, coach Bob Bradley looks like he'll have to choose a new center back pairing for Saturday. Oguchi Onyewu is suspended for yellow-card accumulation, while Jay DeMerit missed training on Thursday with a groin strain. In their place, the most likely scenario calls for captain Carlos Bocanegra to move back to the center from the left side and be paired with Chad Marshall, who's new to World Cup qualifying but played well in the CONCACAF Gold Cup.

When the U.S. faces a trickier game in Port of Spain next Wednesday, the Yanks' depth no doubt will be challenged again, not least because nine players are one yellow card against El Salvador away from a one-game suspension: Jozy Altidore, Bocanegra, Steve Cherundolo, Ricardo Clark, DeMerit, ClintDempsey, Landon Donovan, Benny Feilhaber and Conor Casey.

But the biggest test of the U.S.' depth against El Salvador may come as the result of Bradley's own lineup decisions in a game where the U.S. figures to attack far more than it did against Mexico last month. Tim Howard is a lock to start in goal, but the back line, the midfield and the front line could all see changes to the lineup that started in Mexico City just 2½ weeks ago:

• Defense. Bocanegra and Marshall appear to be likely starters in the central defense. I also expect to see Jonathan Spector return to right back in place of Cherundolo. Spector has been playing regularly at West Ham (albeit at left back) and performed well on the right at the Confederations Cup, while Cherundolo struggled defensively in Mexico. On the left, I expect we'll see JonathanBornstein, the only remaining player whose main position is left back.

• Midfield. The only locks here are Donovan, whom Bradley seems to have decided fits best on the wing, and Michael Bradley, who figures to start even though he has played only 45 minutes of club soccer since the Mexico game.

Keep in mind, though, the onus is on the U.S. to attack what should be a conservative defensive strategy by El Salvador (Los Cuscatlecos have bunkered in their last three road qualifiers, losing all of them 1-0). As a result, the word around camp is that we might not see Clark start next to Bradley, but rather Feilhaber in a central attacking role in front of Bradley. If that's the case, it would be a big chance for Feilhaber to continue the resurgence that started at the Confederations Cup (you'll recall that it was Feilhaber's passes that sprung the U.S.' second goal against Spain and Altidore's penalty against Italy).

Another intriguing piece of camp info: Altidore may not yet be fully ready for 90 minutes of international soccer after training very little on the ball between the Confederations Cup final (on June 28) and the Mexico game, an issue that got extended when Altidore's visa problems kept him from joining Hull City for its first two Premier League games. One possibility for Saturday involves moving Dempsey to forward (see below), where he has played recently for Fulham, and starting Stuart Holden on the right wing, where he impressed for much of the Gold Cup and as a sub at the Azteca.

• Forward. Charlie Davies has been on fire of late, scoring a well-taken goal at Mexico and getting off to a good start at French club Sochaux (including two goals against defending champ Bordeaux and a drawn penalty against Monaco last weekend). If Dempsey moves to the front line, it's very likely we'd see Altidore come on as a second-half sub, with Dempsey moving to Holden's spot in midfield.

Ultimately, the task against El Salvador isn't complicated: The U.S. must win this game and has no business qualifying for the World Cup if it can't hold serve on home soil against one of the region's weaker teams. Building a first-half lead (and not just sitting on it) would certainly relieve much of the angst that would come if the U.S. goes into the halftime locker room without an advantage on the scoreboard.

The history of U.S. vs. El Salvador isn't all that colorful, except for the time in 1997 when John Harkes and Roy Wegerle were approached to throw the World Cup qualifier between the two teams in frigid Foxboro, Mass. (one of my first assignments for Sports Illustrated, by the way). ... If you get a chance, check out my sit-down with former U.S. folk hero Clint Mathis. ... Teaser Alert: I had an hour-plus sit-down with Bob Bradley on Thursday in which he explained many of his world views regarding soccer and strategy. Keep an eye out for it on SI.com next week before the Trinidad and Tobago game ... Casey will not be on hand for the game against El Salvador after having a procedure done earlier this week on his wisdom teeth. ... Altidore doesn't appear concerned about playing time after Hull City's signing of forward Jan Vennegoor of Hesselink (owner of the greatest name ever for the back of a jersey). Said Altidore: "I don't see it as anything but a plus. He's a seasoned guy, he's played in a lot of places, he just came from a big club at Celtic. I think he has a lot to bring to the table and he's a different type of forward. Under the radar, we've become a more dangerous team."

Check back on Saturday before and after the game for SI.com's coverage of U.S.-El Salvador with the estimable Jonah Freedman and I reporting from Rio Tinto Stadium.

Grant Wahl's New York Times best-seller, The Beckham Experiment, is in bookstores everywhere. You can order it here. You can also find him on Twitter.