As a result of the punishment, Smart will be out of the lineup when the Celtics play the Charlotte Hornets on Wednesday at 7:30 p.m. ET.
Celtics head coach Brad Stevens thought the timing of the announcement was a bit unfortunate with roughly two hours until tipoff to reconfigure his lineup.
"I'd agree with that," Stevens said. "I knew they were looking into it but I thought when we got [to] the late afternoon, there wouldn't be anything."
Boston was already set to be without Kemba Walker because of an oblique strain.
Smart's suspension-worthy actions came in Tuesday's 119-115 loss to the Oklahoma City Thunder. His frustrations at the official may have manifested from his own poor performance. The seventh-year veteran shot 4-of-17 from the floor and 1-of-10 from three-point range en route to a 14-point night.
While not a massive setback in the bigger picture, the NBA's decision represents yet another hurdle for the Celtics a season that hasn't gone according to plan. As the team prepares to take the court against Charlotte, it sits sixth in the Eastern Conference at 32-30 and owns the same record as the seventh-place Miami Heat.
Falling into the play-in tournament is a very real possibility for Stevens' squad.