The five-time All-Star underwent a procedure to repair an injury to the tendon in his left thumb following this past NBA campaign and hasn't been cleared to return to play.
Lowry was present at Team USA's recent training camp in Las Vegas but didn't participate in any basketball-related activities. He was a member of the United States' gold-medal squad at the 2016 Olympics.
The 33-year-old was a key component in the Raptors' title run, averaging 15 points, 6.6 assists, and 4.9 boards during the postseason.
Lowry enters the 2019-20 NBA campaign on an expiring three-year, $100-million contract signed during the 2017 offseason.
The Americans will hold their first practice in Los Angeles on Tuesday at the Lakers' practice facility.
Lowry's absence leaves the United States with 15 players remaining for 12 World Cup roster spots.