Defenders Cameron Carter-Vickers and Chris Richards will miss the United States' last two World Cup warm-up matches because of injuries.
The pair was replaced Sunday by Mark McKenzie and Erik Palmer-Brown, who join Walker Zimmerman and Aaron Long as central defenders for exhibitions against Japan on Friday in Dusseldorf, Germany, and Saudi Arabia four days later in Murcia, Spain.
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Goalkeeper Zack Steffen, left back Antonee Robinson, midfielders Yunus Musah and Cristian Roldan, and winger Tim Weah also are missing the matches because of injuries. Central defender Miles Robinson is sidelined through the World Cup because of a torn left Achilles.
Carter-Vickers was left out of Glasgow Celtic's team for its Scottish Premier League game on Sunday, a 2-0 loss to St. Mirren that ended a 38-game unbeaten run in the league. Celtic manager Ange Postecoglou said the center back "pulled up sore" earlier this week.
"We are hoping post-international break he won't be too far away," Postecoglou said.
Carter-Vickers played the full game for Celtic in its 1-1 draw against Ukrainian team Shakhtar Donetsk in the Champions League on Wednesday.
A son of former NBA player Howard Carter, the 24-year-old Carter-Vickers is hoping to secure a spot on the U.S. World Cup roster. He returned to the national team for the first time in three years for a June 1 exhibition against Morocco, his 17th international appearance.
McKenzie, 23, has made eight international appearances and plays for Belgium's Genk. The 25-year-old Palmer-Brown plays for France's Troyes and has made four international appearances.
Back in the World Cup after missing the 2018 tournament, the U.S. opens against Wales on Nov. 21, plays England in a Black Friday matchup four days later and closes group play on Nov. 29 against Iran.
U.S. coach Gregg Berhalter plans to announced his Cup roster on Nov. 9, five days before the deadline to submit it to FIFA.