The Tennessee Titans have suspended in-person club activities after eight positive tests for coronavirus.
Three Titans players and five personnel officials returned positive COVID-19 tests, the NFL announced.
The Minnesota Vikings, whom the Titans defeated 31-30 on Sunday, have also put a halt to in-person activities.
"Out of the abundance of caution, the organisation has decided to work remotely today as we follow NFL protocols related to the COVID-19 virus," the Titans said in a statement.
"Several tests have come back positive and [we] are working through the process of confirming them. We will have more information tomorrow [Wednesday]."
An NFL and NFL Players Association (NFLPA) statement added: "On Tuesday morning, the Titans COVID testing results returned three new player positives and five new personnel positives. The Titans will suspend in-person club activities starting today. Likewise the Vikings, who played the Titans on Sunday, will also suspend in-person club activities.
"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. We will continue to share updates as more information becomes available."
The Vikings said in a statement: "Today the NFL notified us that members of the Tennessee Titans organisation have tested positive for COVID-19. As of this morning, we have not received any positive results from Vikings testing following Sunday's game.
"Per the NFL protocol, we will suspend in-person club activities and close TCO Performance Center immediately. We will work closely with the NFL and NFLPA to monitor the situation, perform additional testing and determine when the facility can reopen. We will provide further updates regarding this week's football schedule when appropriate."
ESPN reported the Titans' facility will be shut down until Saturday, throwing their Week 4 clash with the Pittsburgh Steelers on Sunday into doubt.
The Vikings are scheduled to face the Houston Texans on Sunday.