Both left backs on the U.S. squad are likely to miss the Americans' opening World Cup qualifier against Antigua and Barbuda on Friday.

Edgar Castillo injured a hamstring or groin during training on Thursday, according to U.S. coach Jurgen Klinsmann. Castillo started Sunday's 0-0 friendly draw at Canada when Fabian Johnson strained a calf muscle during warmups.

Klinsmann says Johnson is doubtful for Friday but could possibly return for Tuesday's qualifier at Guatemala.

Captain Carlos Bocanegra could shift to the left, leaving Oguchi Onyewu, Michael Parkhurst or Geoff Cameron to join Clarence Goodson in the center.