Horford missed his second straight game with a bruised back after crashing to the floor on Friday night following a flagrant foul by the Clippers' Blake Griffin.
Zaza Pachulia replaced Horford in the starting lineup and tallied just two points and two rebounds in Atlanta's 117-83 loss to Philadelphia.
Asked after the game how he feels, Horford said, "Not too good."
Coach Larry Drew says Horford's back was still sore when he tried to join the team's shooting practice on Tuesday. Drew says it was the smart decision to give Horford another day off because the team doesn't play again until Saturday against Charlotte.
Horford is averaging 16.2 points and 9.9 rebounds and has started all 48 games he has played this season.
Information from The Associated Press was used in this report.