The game was postponed in accordance with the league's health and safety guidelines as the 76ers don't meet the minimum roster requirement of eight players.
The contact tracing is connected to Saturday's loss to the Memphis Grizzlies, sources told ESPN's Adrian Wojnarowski.
The Grizzlies listed Jonas Valanciunas as out for Monday's game against the Phoenix Suns as the center has entered the league's health and safety protocols. The Grizzlies played the Minnesota Timberwolves on Wednesday before their game on Friday was postponed due to contact tracing within the Wolves. Karl-Anthony Towns announced that he tested positive for COVID-19 on Friday.
The Sixers have been battling against a postponement for more than a week after guard Seth Curry tested positive for COVID-19 on Jan. 7. They played with only eight players on Jan. 9 against the Nuggets.
They used just nine players in Saturday's loss and had six listed on their injury report. Two were out due to health and safety protocols (Curry and Vincent Poirier) with Joel Embiid (knee), Furkan Korkmaz (groin) and Mike Scott (knee) sitting with injuries. That would leave six other players out Sunday because of contact tracing.
The Sixers are next scheduled to host the Boston Celtics on Wednesday night.