The Celtics were scheduled to face the Bulls at 8 p.m. EST on Tuesday in Chicago. The Mavericks were scheduled to host the Pelicans on Monday in Dallas.
Sources told ESPN and the Dallas Morning News on Monday that four Mavericks players had tested positive for COVID-19. The team also shuttered its facility on Sunday. The Celtics still don't have enough players to play a game due to the league's COVID-19 protocol.
"The NBA and NBPA will be meeting today about modifying the league's health and safety protocols," the NBA said in a news release.
The Celtics are scheduled to host the Magic on Wednesday in Boston. The Bulls are scheduled to battle the Oklahoma City Thunder on Friday in Oklahoma City.
The NBA announced a shortened 72-game schedule in November for the 2020-21 campaign. The first half of the season started on Dec. 22 and ends March 4. The second half is from March 11 to May 16.
Each team has three games against each opponent in their respective conference for a total of 42 games apiece. Teams also play two games against each opponent from the alternate conference.