For the first couple of months of the N.B.A. season, the league operated with something that approximated business as usual: full arenas and full rosters as teams adapted to the new normal of playing through the coronavirus pandemic.

But amid a recent surge of players and coaches who have landed in the N.B.A.’s Covid-19 health and safety protocols, the league finds itself contending with some familiar challenges and concerns.

Positive tests. Canceled practices. And the looming possibility of more postponed games, just as the N.B.A. approaches what some fans consider its real opening day: a five-game slate on Christmas Day.

On Tuesday, the Nets announced that six more players, including James Harden, had joined Paul Millsap in the protocols, meaning they had tested positive for the coronavirus or had been in close contact with someone who had. That left the Nets with a very short rotation for their home game against the Toronto Raptors on Tuesday night. The Los Angeles Lakers, meanwhile, canceled their practice after Talen Horton-Tucker entered the protocols ahead of the team’s flight to Dallas for a game against the Mavericks on Wednesday.

Once in the protocols, players cannot return to play until they have isolated for 10 days or returned two negative test results at least 24 hours apart.

Those developments came one day after the league announced that it was postponing a pair of Chicago Bulls games this week after 10 of the team’s players, as well as other staff members, landed in the protocols. Those two games — against the Detroit Pistons on Tuesday and the Raptors on Thursday — were the league’s first postponements of the season.

“Like the rest of the country, and as was predicted by our infectious disease specialists, we have seen an increase of cases around the league,” said Mike Bass, an N.B.A. spokesman. “As we have since the pandemic began in March 2020, we will continue to follow the science and data, and will, in close partnership with the players’ association, update our protocols as deemed appropriate by our medical experts.”

All of the Bulls’ players have been vaccinated, according to two league sources who requested anonymity because they were not authorized to publicly discuss the players’ vaccination statuses.

The league has said that more than 97 percent of its players are fully vaccinated, and that more than 60 percent of those eligible have received booster shots. The players’ union did not agree to a vaccine mandate before the start of the season. A few players, such as the Nets’ Kyrie Irving and Washington’s Bradley Beal, have spoken out about not wanting to get vaccinated.

Last season, the league and the players’ union reported more than 75 positive tests among players, most of them before vaccines were widely available. More than 30 games were postponed.

Given the possibility that players might have been exposed to the virus during Thanksgiving gatherings this year, the league and union agreed to institute mandatory testing on Nov. 28, 29 and 30. Before then, vaccinated players were being tested only if they exhibited symptoms or had been around someone who had tested positive.

CJ McCollum, the president of the players’ union, told The New York Times recently that he was encouraging players to get vaccines and booster shots, and that he doesn’t allow unvaccinated people into his home. Extra testing, he said, “just makes sense.”

“I think when we explain to people the importance of knowing — there’s a lot of things that go under the radar in terms of being positive, but being asymptomatic,” he said. “So I think testing around the holidays when people are flying or traveling, families are coming in from out of town, you’re gathering, you’re more exposed.”

Since Thanksgiving, the league has seen an uptick in the number of positive cases among players and personnel. Last week, the Indiana Pacers and the Raptors each canceled practices out of what both teams described as an “abundance of caution.” The Charlotte Hornets had several players in the protocols, including their best player, LaMelo Ball, who won the N.B.A.’s Rookie of the Year Award last season.

And earlier this week, two members of the Raptors’ broadcasting crew volunteered to step away from their duties after they learned that they had been exposed to someone outside of the Raptors organization who had tested positive.

The Lakers’ LeBron James was in the protocols earlier this month after he tested positive. Follow-up tests were negative, indicating that the first test was a false positive. James said before the season that he had been vaccinated.

Sopan Deb and Tania Ganguli contributed to this report.