Brown posted 22 points and 11 rebounds before exiting.
The loss of the former California Golden Bear is the latest setback in a 2020-21 season where little has gone right for the Celtics.
Kemba Walker's season debut was delayed due to his recovery from a stem cell procedure on his knee. A calf strain sidelined Marcus Smart. Jayson Tatum was diagnosed with COVID-19 and acknowledged some lingering effects of the virus remained after he returned to the court.
As a result, Boston sits eighth in the Eastern Conference at 23-25.
Brown has been one of the team's standout performers. He's averaging 24.5 points, 5.6 rebounds and 3.7 assists through 44 appearances. His positional flexibility has been invaluable as well since the Celtics failed to adequately replace Gordon Hayward on the wing following his sign-and-trade to the Charlotte Hornets.
Losing the 24-year-old for any stretch of time will put serious strain on a roster that didn't have a wealth of depth to begin with.