Raptors guard Fred VanVleet was listed as unavailable for Toronto's game Monday against the visiting Atlanta Hawks.
Coach Nick Nurse said VanVleet didn't participate in Sunday's practice due to lower back tightness.
Nurse said rookie Christian Koloko would be slotted into the starting lineup.
VanVleet struggled in Friday's 112-90 loss to Philadelphia, shooting 0-for-11, including eight missed three-pointers. His single point came on a free throw.
The 28-year-old, who earned all-star honours for the first time last season, is averaging 13.3 points, 7.7 assists and 4.0 rebounds per game.
