Eight Vikings players, one coach and three staff members returned presumptive positive tests for COVID-19 on Sunday, on the same morning teams around the NFL were reporting false positive tests in connection with a lab in New Jersey the league has used to process daily test results for some teams.

Coach Mike Zimmer said the Vikings' 12 affected people quarantined Sunday and watched the Vikings' team meetings virtually instead of practicing. Further testing should give the Vikings additional clarity Monday as to whether the players actually have COVID-19.

The Associated Press reported Sunday night that the NFL had 77 positive COVID-19 tests from 11 teams re-examined by the New Jersey lab after false positives, and all those tests came back negative. The league asked the New Jersey lab BioReference to investigate the results, and those 77 tests are being re-tested once more to make sure they were false positives.

Citing 90-degree temperatures, the Vikings moved Sunday's practice indoors. This season's NFL media policy allows only reporters who have gone through COVID-19 testing to step inside a team facility; the Vikings have so far tested one reporter not affiliated with the team or league to file pool reports during indoor training camp practices.

According to Sunday's pool report, eight players were not present at practice: linebacker Eric Kendricks, defensive ends Jalyn Holmes and Kenny Willekes, fullback C.J. Ham, wide receivers Dillon Mitchell and Alexander Hollins, tight end Nakia Griffin-Stewart and tackle Ezra Cleveland. Assistant special teams coach Ryan Ficken was also absent.

"If these all turn out negative, then there was a problem at the lab," Zimmer said. "Obviously, if they're positive, there might be a problem with things we're doing, or other teams are doing, or whatever. It's hard for me to speculate now on what it is or what it was."

The Vikings were one of at least 10 teams affected by a spate of positive tests that caused teams to change their plans. The Jets canceled a walk-through on Saturday night after reporting 10 false positive tests, and the Bears moved their Sunday morning practice to the afternoon following nine false positives.

The Browns canceled practice, before reopening their facility once their tests were found to be false, and the Steelers announced they had six players held out of practice because of "adherence to the COVID-19 protocol," though they said none of their players needed to go on the league's COVID-19 reserve list.

Packers coach Matt LaFleur told reporters the team had a couple of players affected by the testing results but was able to catch false positives before practice and get all of the players on the field who were supposed to practice.

"Saturday's daily COVID testing returned several positives tests from each of the clubs serviced by the same laboratory in New Jersey," the league said in a statement Sunday morning. "We are working with our testing partner, BioReference, to investigate these results, while the clubs work to confirm or rule out the positive tests. Clubs are taking immediate precautionary measures as outlined in the NFL-NFLPA's health and safety protocols to include contact tracing, isolation of individuals and temporarily adjusting the schedule, where appropriate. The other laboratories used for NFL testing have not had similar results."

"Definitely probably better that this happened now than three weeks from now," Buffalo Bills general manager Brandon Beane, whose club had some of those positive results, told The Associated Press. "But it seems like every few weeks, or even every week, something's going on. Who know what the next curveball will be?"

Beane said tests had gone "haywire," and called it "a lab issue and not a true issue with our guys currently" after several Bills were held out of practice.

While the Bears said they have a lab in Minnesota involved in their testing process, Zimmer said the Vikings do not send tests to a lab in Minnesota. He added he believes the Vikings' tests on Sunday will go back to the same New Jersey lab.

In the meantime, the Vikings will move forward with practice and hope further testing shows the 12 affected people don't have COVID-19.

"Honestly, for us, it's probably good that it happened now," Zimmer said. "We were able to adjust and adapt and figure out the kinds of things that would happen if it did happen during the season and what we would do from there."