CARSON, California — As it prepares to play its first game of the year, the United States men's football team faces unexpected tests of its depth.

Seven members of the original squad for Saturday's friendly against Sweden in Carson have left camp due to injuries, overseas trials or other reasons.

Coach Bob Bradley takes it in stride.

"You expect some difficulties," Bradley said. "The road is never smooth from start to finish. Other than that, the guys have come in with a very good attitude and we feel it's been a very good camp."

All but two of Bradley's players come from Major League Soccer. Only Houston Dynamo forward Brian Ching has played in as many as 20 games for the United States; six have yet to make their international debuts.

But with most of the United States' regular starters — including Landon Donovan, Tim Howard, Carlos Bocanegra and Oguchi Onyewu — competing overseas, Bradley wants to evaluate other players before the first World Cup qualifier Feb. 11 against Mexico in Columbus, Ohio.

"This camp is essential because MLS players who have been off need time to get ready for games," Bradley said. "If you have four or five guys that you feel may be in the mix for Mexico, this whole month is necessary to have them ready."

Newcomers include forward Charlie Davies, who scored 14 goals in 27 games for Hammarby in Sweden's first division last year, and the Chicago Fire's Jon Busch, MLS goalkeeper of the year.

But among the missing are three of the league's best young players.

Defenders Chad Marshall of the Columbus Crew and Sean Franklin from the Los Angeles Galaxy left camp with a sprained right knee and a hernia, respectively. Franklin was the MLS rookie of the year, Marshall its defender of the year.

Chivas USA midfielder Sacha Kljestan, who played in the 2008 Olympics and joined Marshall on the MLS Best 11, left camp Thursday for a one-week trial with perennial Scottish power Glasgow Celtic. Kljestan is expected back Jan. 22.

Another player, goalkeeper Troy Perkins, returned to Valerenga IF in Norway for mandatory team exercises with Norwegian Special Forces. Colorado Rapids defender Cory Gibbs declined to attend the national team camp at all.

Replacing them are San Jose Earthquakes defender Jason Hernandez, Rapids defender Ugo Ihemelu and Chivas USA goalkeeper Dan Kennedy.

Despite the flurry of recent changes, Bradley said he sees general progress.

"We always look at the whole picture," Bradley said. "We're growing as a team. Our mentality has gotten stronger. Tactically, the players have a good understanding of how we play in order to be successful."