Bryant apparently injured his shoulder during practice Tuesday, coach Mike Brown said. The injury isn't thought to be serious, and Bryant wanted to play against the Trail Blazers, Brown said.
Jodie Meeks is likely to take Bryant's spot in the Lakers' starting lineup.
Bryant missed a day of practice last week with soreness in his right foot. The fifth-leading scorer in NBA history is beginning his 17th season in the league.
The Lakers faced Portland without center Dwight Howard, who is cautiously returning from offseason back surgery. Howard is practicing with the Lakers and participated in a pregame workout with his teammates at Citizens Business Bank Arena.