Lopez informed USA Basketball officials Wednesday that he didn't believe he was in good enough condition to take part in training camp next week in New York.
He played poorly during practices in Las Vegas last month and USA Basketball chairman Jerry Colangelo said he would have to perform well during the second training session to have a chance to make the roster headed to Turkey for the world championships.
Instead, Lopez became the latest big man on an undersized U.S. roster to withdraw. The Americans lost Amare Stoudemire, David Lee and Robin Lopez, Brook's brother, shortly after opening camp in Las Vegas. They were already without Boston's Kendrick Perkins, who injured his knee in Game 6 of the NBA Finals.
"Although it will be disappointing not to see Brook compete in the upcoming FIBA world championship, the Nets fully support his decision to stop training with Team USA," Nets general manager Billy King said in a statement.
"Brook obviously felt that he had not made sufficient enough recovery from his bout with mononucleosis earlier this summer, but we feel confident he will be fully recovered by the start of training camp on September 25."
Tyson Chandler and McGee are the only centers on the roster. McGee had practiced in Las Vegas with the Americans the last two summers, but hadn't officially been added to the national team.