Even though most games have been played without fans in the stands, the NFL had navigated the novel coronavirus pandemic with relative smoothness through three weeks of the regular season. That changed before Week 4.

Early in the week, news broke that eight members of the Tennessee Titans — three players and five staff members — had tested positive for the coronavirus in the aftermath of their Week 3 game against the Minnesota Vikings, with more players and staff members testing positive as the week wore on. The development injected uncertainty into the schedule for the first time since the summer, when the pandemic forced the cancellation of preseason games and required teams to significantly alter how they went about their daily operations.

Additional positive tests within the organization have since been announced. So after announcing Wednesday that the Titans’ game against the Pittsburgh Steelers would be rescheduled for Monday or Tuesday, the league opted Thursday to postpone the game until later in the season.

Here’s what else we know about the situation.

How often are NFL players tested?

NFL players are tested daily during the regular season except on game days, with the final testing before games done the morning before. Any coach, player or staffer who has an inconclusive result from the test taken the day before the game can be cleared to play with a negative test result on game day, provided that the result is available at least two hours before kickoff.

On Friday, the NFL and the players’ union announced that daily testing — except on game days — will continue indefinitely. The league also announced that players and coaches will not be allowed to leave their cities during their bye weeks.

What happens if a player tests positive?

If a player tests positive, what happens next depends on whether he is showing symptoms of covid-19, the disease caused by the coronavirus, or is asymptomatic.

If a player tests positive and is showing symptoms: The player cannot return until at least 10 days have passed since the symptoms first appeared and until at least 72 hours have passed since the symptoms last occurred. The player’s return must be approved by the team physician after consultation with the NFL’s chief medical officer and must adhere to local regulations.

If a player tests positive and is not showing symptoms: The player cannot return until 10 days have passed since the initial positive test or five days have passed since the initial positive test and the player tests negative in consecutive PCR tests separated by 24 hours. The player’s return must be approved by the team physician after consultation with the NFL’s chief medical officer.

What is the covid-19 reserve list?

Players who test positive or who have been quarantined after having been in close contact with an infected person or people are placed on the covid-19 reserve list, a new category of injured reserve created this season.

On Tuesday afternoon, Tennessee placed defensive lineman DaQuan Jones, long snapper Beau Brinkley and tight end Tommy Hudson on its covid-19 reserve list. On Wednesday the team added linebacker Kamalei Correa. Under terms of an agreement between the league and the players’ union, teams may not disclose why the players were placed on the list (in other words, whether they tested positive or have been quarantined because of potential exposure to the coronavirus).

The players may return to the team when healthy or out of quarantine.

What happened with the Titans and Vikings?

The Titans, who defeated the Vikings on Sunday in Minneapolis, shut down in-person activities Tuesday after three players and five team staff members tested positive for the coronavirus, the NFL and the players’ union announced. One more Tennessee player learned Wednesday morning that he had tested positive, according to an NFL spokesman, and on Thursday the league announced that another player and another staff member had tested positive. Two more Titans players learned of positive tests on Friday, and the team saw more positive cases on Saturday — one more player and two staffers —which brought the team’s total to 16.

Titans Coach Mike Vrabel had said Monday that outside linebackers coach Shane Bowen was placed in the team’s covid-19 protocol after test results came in Saturday morning. Bowen, who calls the Titans’ defensive plays, did not travel with the team to Minnesota.

The Vikings have not had any positive tests this week, per numerous reports, on Thursday restarted in-person training at their team facility.

What does this mean for Week 4?

The Titans were scheduled to host the Steelers on Sunday, but the NFL announced Friday that the game has been rescheduled for Week 7 (Oct. 25 at 1 p.m. Eastern). Week 4 now will be the bye week for Tennessee and Pittsburgh.

Tennessee was supposed to have a bye and the Steelers were to face the Ravens in Week 7, which now will be Baltimore’s bye week. The Ravens and Steelers now will play Week 8 (Nov. 1 at 1 p.m. Eastern).

On Friday, ESPN’s Turron Davenport reported that the Titans’ Week 5 game against the Buffalo Bills “could be seriously in jeopardy” as more positive tests come in. Tennessee’s team facility will remain closed through the weekend.

Minnesota remained scheduled to play Houston on Sunday.