PRINCETON - The one thing the central defense has in common as the U.S. team prepares for the World Cup is the last thing the Americans need: injuries.

How well Oguchi Onyewu, Jay DeMerit and Carlos Bocanegra overcome their injuries will be key to the Americans' chances in South Africa.

Bocanegra underwent sports hernia surgery May 5 in Germany, DeMerit has been battling an abdominal strain, and Onyewu is coming off a major left knee injury last October and hasn't been in a game since.

The coaching staff, and the players themselves, are eager to see what level of game fitness each is at as the United States plays the Czech Republic on Tuesday in East Hartford, Conn., and Turkey on Saturday at Lincoln Financial Field before heading to South Africa.

The Americans have a friendly against Australia on June 5 in Roodepoort, South Africa. Their World Cup opener is one week later against England, 3-1 winners over Mexico in a friendly at Wembley on Monday.

"I don't think the games are any rougher," Onyewu said Sunday on the final day of training camp at Princeton University. "There will be injuries, you know that, leading up to this."

Bocanegra's was the most recent injury, and coach Bob Bradley only revealed Saturday that the team captain had surgery two weeks ago. The central back, who turns 31 on Tuesday, hopes to be in the lineup in Connecticut, for his birthday.

"I don't think it's a big issue," Bocanegra said Sunday. "I thought it would be best to get the little procedure done as soon as possible. I was running three days after."

Bocanegra was hurt March 28 while playing for Rennes of the French league. He was kicked just above the left knee, and for several days couldn't flex his leg. He compensated for the pain by putting stress on other areas of his body, and that caused abdominal problems.

He sat out a match May 2 and then had the surgery after consulting with doctors.

Now comes a few days of sorting out the back line - as well as the rest of the squad. Bradley must trim from 30 players to a final roster of 23.