Celtics coach Doc Rivers told reporters before the game that the 17-year veteran didn't look good in practice on Friday, so the team decided to sit him.
"Kevin's not playing tonight," Rivers said. "Not because it's a night off, just because he wasn't running well at practice."
When asked if he expected it to be longer, Rivers said, "No, I don't think so."
Boston already lost Rajon Rondo, Jared Sullinger and Leandro Barbosa for the season. Barbosa was later traded to Washington at the deadline.
Rondo and Barbosa suffered season-ending knee injuries. Sullinger underwent back surgery.
Jeff Green was expected to start in place of Garnett.
Garnett has played 63 of the team's 64 games this season, only missing a win in Phoenix when he was rested after attending the All-Star game.