The Chicago Bulls’ next two games — against the Detroit Pistons and Toronto Raptors — have been postponed because 10 Bulls players, as well as other staff members, are in the league’s Covid-19 health and safety protocols, the N.B.A. announced Monday. With so many players unavailable, the Bulls faced the prospect of not being able to field enough healthy players to take the floor.

This marks the first postponement of an N.B.A. game this season and a reminder of the coronavirus pandemic’s continuing prevalence. Players enter the protocols when they test positive for the coronavirus or if they are possibly exposed to someone who has. Once players are in the protocols, they must quarantine for 10 days or until they have two negative P.C.R. test results at least 24 hours apart.

The league has seen a striking uptick in the number of players in protocols since increasing testing, even among vaccinated players, after Thanksgiving. Last week, the Indiana Pacers and Raptors separately canceled a practice out of what both teams said was “an abundance of caution.”

Other teams affected by the recent upward swing in cases include the Charlotte Hornets, who had five players listed in protocols last week. On Monday, the team named only two, including their top player, LaMelo Ball.

Before the season, Arturas Karnisovas, the executive vice president of the Bulls, said the team was “getting pretty close” to being fully vaccinated. The league and team did not immediately respond to an inquiry from a reporter about whether all the Bulls players had received the Covid-19 vaccine.

Last season, the pandemic disrupted the N.B.A. right from the start, with dozens of games postponed throughout the season, mostly in January. Only three teams did not have a game postponed: the Los Angeles Lakers, Los Angeles Clippers and the Nets.

Chicago’s next scheduled game is tentatively scheduled for Sunday, when the Bulls host the Lakers. As of Monday, the Bulls were 17-10, and, ranked third in the Eastern Conference, were in the midst of a surprisingly strong start to the season. In the off-season, they added the four-time All-Star guard DeMar DeRozan; guard Lonzo Ball, who had been with the New Orleans Pelicans; and guard Alex Caruso, who had been with the Lakers. DeRozan has missed the past three games because he was in the protocols.

Meanwhile, the N.H.L. postponed three Calgary Flames games after six players and a staffer entered Covid protocols. The Flames are the third N.H.L. team to miss games because of Covid, after the New York Islanders and Ottawa Senators.