The NFL had 77 positive COVID-19 tests from 11 teams re-examined by a New Jersey lab after false positives, and all those tests have come 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.
Among teams reporting false positives, the Minnesota Vikings said they had 12, the New York Jets 10 and the Chicago Bears nine.
The Jets cancelled a walk-through Saturday night but had a full practice Sunday morning after the previously positive tests came back negative. The Bears moved their practice scheduled for Sunday morning to the afternoon.
The Detroit Lions had a player with a false positive test from the same lab in New Jersey and he was held out of practice on Sunday, a league source told The Associated Press. The person spoke on condition of anonymity because the league and team were not disclosing test results.
The Pittsburgh Steelers said they had six false positives and those players will be back at practice on Monday.
The Philadelphia Eagles held out four players from working out on Sunday. The Cleveland Browns initially cancelled practice, but after re-testing turned up negative tests they decided to have their workout.
There are five labs nationwide that service the 32 teams, with only the New Jersey facility having the false positives this weekend.
The number of positive COVID-19 tests from a specific facility that might actually be false demonstrates the precarious position the NFL is in less than three weeks from the regular-season opener.
"Definitely probably better that this happened now than three weeks from now," said Buffalo Bills general manager Brandon Beane, whose club had some of those positive results. "But it seems like every few weeks, or even every week, something's going on. Who knows what the next curveball will be?"
Beane said tests in the Northeast 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.
Anyone testing positive for COVID-19 - even a false positive upon a retest - is required to have two more negative tests before being cleared to return.