Seventy-seven positive coronavirus tests from 11 NFL teams have all been shown to be false positives after they were re-examined by a New Jersey lab.
The NFL asked the lab, BioReference, to investigate the results, and the tests will be re-examined again to ensure accuracy.
Five labs nationwide service the 32 NFL teams. BioReference was responsible for all 77 of the false positives, which forced several teams to alter their pre-season training schedules.
The Minnesota Vikings returned 12 false positives among their players and staff, the New York Jets had 10 and the Chicago Bears had nine.
The Philadelphia Eagles had four players miss out on practice on Sunday after they returned false positives, while the Detroit Lions also had a player forced to sit out, a league source told The Associated Press.
Buffalo Bills general manager Brandon Beane, whose team also had some false positives, said: "Probably better that this happened now than three weeks from now.
"But it seems like every few weeks, or even every week, something's going on. Who knows what the next curveball will be?
"We had an open dialogue with our players. We even had some of our leadership crew of players on with Dr [Allen] Sills [the NFL's chief medical officer] this morning, just hearing directly with him, who's aware of all these tests that have gone a little bit haywire here in the north-east.
"I think that was good for them to hear because naturally, if you're going to be out there tackling and blocking and things like that, passing the ball around, people might be unnerved if we got some guys missing."
Prior to Sunday's announcement, coronavirus numbers in the NFL were getting smaller, with four players listed on the COVID-19 list on Saturday.
The Kansas City Chiefs are scheduled to host the Houston Texans in the NFL's first game of the season on September 11, with full coverage of the new campaign live on Sky Sports.
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