NEW YORK (AP/KDKA) — The NFL revealed Sunday that several positive COVID-19 tests were found a day earlier by one of its testing partners, and the Chicago Bears said they had nine false positives.

The league has asked the New Jersey lab BioReference to investigate the results “while the clubs work to confirm or rule out the positive tests.” The NFL did not identify the teams or say how many tests were positive.

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Two teams, Washington and Detroit, said they are practicing Sunday, while Cleveland has called off its workout.

The Steelers held six players out of practice on Saturday and according to General Manager Kevin Colbert, they will return tomorrow.

The NFL uses BioReference for all of its COVID-19 testing, though tests are handled by labs throughout the nation to ensure teams get results quickly — hopefully within 24 hours. Heading into this weekend, there had been four confirmed positive tests for players who were at training camps.

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“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 NFL said in a statement. “The other laboratories used for NFL testing have not had similar results.”

The Bears moved their practice scheduled for Sunday morning to the afternoon.

“This morning we learned yesterday’s COVID-19 testing identified nine players/staff as positive,” the Bears’ statement said. “We followed additional NFL-NFLPA testing protocol and confirmed all nine results as false positives.”

The Browns said initial results from the lab indicated multiple “presumptive positive cases” that included coaches, players and staff.

“Although, we have received indication from the NFL that they are investigating irregularities in lab results that have also impacted other clubs, out of an abundance of caution, we will immediately follow our comprehensive Infectious Disease Emergency Response plan, and pause any activity in our building today and conduct meetings virtually,” a Browns spokesman said. “As per plan procedure, the team is also diligently reviewing proximity data for contact tracing and instructed self-isolation for those who tested positive and others as appropriate, even though they all remain asymptomatic.

“Our facility is currently undergoing a thorough deep-cleaning and disinfecting process and is closed to all personnel for the day.”

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