The Vikings suspended activities at their team facility for at least two days after learning Tuesday morning that three players and five staffers from the Tennessee Titans, the Vikings’ opponent last Sunday, tested positive for COVID-19.

“The Titans will suspend in-person activities starting today. Likewise, the Vikings, who played the Titans on Sunday, also will suspend in-person club activities,” the NFL said in a statement. “Both clubs are working closely with the NFL and NFLPA, including our infectious disease experts, to evaluate close contacts, perform additional testing and monitor developments. All decisions will be made with health and safety as our primary consideration.”

In response to the NFL’s first team outbreak of this pandemic season, Commissioner Roger Goodell sent a memo to teams Tuesday, saying, “This is not unexpected” and noting that league doctors have emphasized that “there will be players and staff who will test positive during the season.”

In a statement Tuesday, the Vikings said no players have tested positive since Sunday’s game as of Tuesday morning.

Vikings employees started the day at the club’s facility in Eagan with daily testing before the NFL announced the shutdown shortly before 10 a.m. The Vikings also are closing their facility Wednesday, when they would have returned to practice for Sunday’s game against the Texans. According to several news media reports, the Titans suspended in-person activities through Friday.

It remains to be seen if the Titans’ positive results will affect the Vikings game in Houston or the Titans’ home game against Pittsburgh on Sunday. Steelers coach Mike Tomlin said his team has been "given a mandate" to prepare as if the game will be played on time — even if the Titans are unable to practice.

The Steelers said in a statement, “We have been informed to proceed with our game preparations for Sunday’s game until we are informed otherwise.”

The Vikings are planning to keep testing throughout the week even if the facility is closed. Vikings General Manager Rick Spielman and head athletic trainer Eric Sugarman, who is in charge of COVID-19 protocols, are scheduled to appear on a videoconference Wednesday morning to provide an update.

Tennessee beat the Vikings 31-30 at U.S. Bank Stadium on Sunday afternoon. The Titans played that game without linebackers coach Shane Bowen, who was put in the NFL’s COVID-19 protocol after receiving positive test results Saturday and did not travel to the Twin Cities with the team, Tennessee coach Mike Vrabel said Monday.

On Tuesday, the Titans placed three players — starting nose tackle DaQuan Jones, long snapper Beau Brinkley and practice-squad tight end Tommy Hudson — on the COVID reserve list, which is for players who test positive or are in quarantine for being in close contact with an infected person.

Jones played 69% of the Titans’ defensive snaps Sunday against the Vikings, and six snaps on special teams. He was credited with two tackles and one quarterback hit.

Brinkley was on the field for 10 snaps on a busy day for the Titans’ special teams, which got six field goals from Stephen Gostkowski.

The NFL’s COVID-19 testing protocol requires individuals who tested positive to have two additional tests to confirm if the initial positive test result was accurate. ESPN, citing a league source, reported that all eight positive tests have been confirmed positive. Vrabel said the Titans were following league protocol with regard to contact tracing.

The league does daily PCR tests from Monday through Saturday, with results usually available within 24 hours, but it does not test on game days as part of the agreed-upon protocol between the NFL and NFLPA.

A PCR test on a Sunday would not deliver results quickly enough to confirm whether a player is positive, and point-of-care tests with rapid results would put teams in the position of quarantining players or coaches on a game day based on a test that might not be as reliable.

The novel coronavirus has an incubation period of up to 14 days, and it can take several days after exposure for the virus to register on a test.

Tuesday’s developments underscore the challenge of playing sports in a pandemic without a bubble. Major League Baseball and college football have had to manage outbreaks on teams that led to the postponement or cancellation of dozens of games.

The NFL, though, had largely been spared those problems through the first three weeks of the regular season. Testing results from the week of Sept. 20-26 had not yet become available. For the week of Sept. 13-19, there were no positive results among 14,074 tests given to 2,438 players, and five positive results among 22,590 tests given to 5,407 other personnel. Out of 40,479 tests from Sept. 6-12, the week leading up to the first set of games, there were seven confirmed positives, including two players.

To limit the spread of the virus, the NFL enacted a series of protocols, including canceling the preseason to limit travel.

All NFL road trips come under a bevy of new guidelines that prohibit outside visitors in the hotel, dining at restaurants or riding in public transportation, among other rules. All players and top-level staff wear proximity trackers at team facilities, at practices and during team travel, to record interactions within 6 feet of each other and help with contact tracing.

Teams were given roster flexibility to deal with players getting sick. Practice squad rosters grew from 12 to 16.

The NFL formed an independent advisory committee of former players, coaches and general managers to help make decisions on postponing games because of the pandemic.

But the fact remains that football is a sport where social distancing is impossible. So on Tuesday, Goodell emphasized facility maintenance, minimizing close contacts while traveling and within position groups, players and staff wearing PPE, and regulating behavior outside team activities.

In his memo, Goodell said, “We are exploring in more detail the nature of the close contacts to determine where they occurred (locker room, flights, etc.), and identify any additional learnings that can be shared with all clubs.”

Staff writers Michael Rand and Andrew Kramer contributed to this article.