PRINCETON, N.J. — Just 18 of 30 players were in full practice as the U.S. opened its pre-World Cup training camp.

While three players were off to get physicals Monday and four had not yet arrived from Europe, the greater concern with the Americans' World Cup opener less than a month away was the quintet of injured players.

Goalkeeper Tim Howard (quadriceps strain), defender Jay DeMerit (abdominal strain), forward Eddie Johnson (hamstring strain) and defender Chad Marshall (slight hamstring strain) were in the trainer's room instead of Roberts Stadium. Defender Carlos Bocanegra (abdominal strain) worked out on his own.

U.S. coach Bob Bradley hopes to cut his roster to the 23-man limit by the time the team arrives in Philadelphia on May 26.