Emily Kaplan of ESPN first reported the postponement.
The Flyers reportedly have "COVID-19 issues," becoming the fifth NHL team to currently be on pause as a result of the pandemic.
The New Jersey Devils, Buffalo Sabres, Minnesota Wild and Colorado Avalanche have all suffered outbreaks of the virus within players and staff and postponed games as a result. The Capitals game is one of three postponed on Tuesday along with Wild-St. Louis Blues and Avalanche-Arizona Coyotes.
The latest change comes less than a week after the NHL revised its COVID-19 protocols.
According to Greg Wyshynski of ESPN, the league had initially mandated that players arrive to the arenas no more than one hour and 45 minutes before game time, but changes were made to suggest players do so "whenever practicable."
The NHL has also made several changes since the start of the 2021 season, including the switch to rapid testing to get results before game time. The removal of glass behind benches was also made to potential improve airflow.
Philadelphia earned a 7-4 win over the Capitals on Sunday but now doesn't have another scheduled game until Feb. 14 after its two games against the Devils were postponed.
Washington will also have an extended break after its games against Buffalo and Philly were postponed. The team is currently set to face the Pittsburgh Penguins on Sunday.