The suspension forced him to miss Wednesday night's 120-111 home win over Charlotte.
Celtics coach Brad Stevens said he found out about Smart's suspension a couple of hours before tip-off.
"I'm not even completely aware of what happened," Stevens said during his pregame media availability. "I did hear there were words after the game."
The NBA did not provide many specifics in a news release beyond saying the incidents with Smart occurred "during and after the Celtics' 119-115 loss to the Oklahoma City Thunder."
"I saw Marcus this morning. We talked about it," Stevens said.
Boston was already short-handed at point guard, with Kemba Walker out with a left oblique strain.
The Associated Press contributed to this report.