The NFL has enacted a policy that will require players and team staff members to isolate if they experience COVID-19 symptoms, even if their most recent test result is negative, chief medical officer Allen Sills said Thursday.

As a result, there will likely be an uptick in missed practices and perhaps games as the team medical staffs work to determine the source of the symptoms. The coming cold and flu season will add a new level of complexity to the task, and will serve as a sharp break in routine for players and coaches who in previous years have routinely pushed through illnesses to get on the field for games.

"We're always going to err on the side of safety and we're going to support the medical judgment of the medical staff," Sills said in a conference call with reporters. "Everyone has the same goal here and that's to operate as safely as we can. ... When you look at the big picture, our goal is to make sure we don't put someone on the field that we think might be actively infected. If we're going to make a mistake, we would rather make a mistake on the side of being cautious and keeping people off the field. If it turns out that those were non-COVID symptoms, I think we would all be happy with that outcome."

Cleveland Browns receiver Odell Beckham Jr. was sent home from the team facility Thursday because of an illness, although Sills did not speak to Beckham's specific situation. There will be no set timetable to guide the return of people asked to isolate under this policy. Instead, Sills said, they will be judged on a "case by case basis" while testing for other ailments such as influenza other respiratory viruses.

Lions running back Adrian Peterson was listed as not practicing Thursday due to an illness. A Lions source told ESPN it is not related to COVID-19. Peterson has been Detroit's leading rusher since signing with the team just before Week 1 with 54 carries for 245 yards and a touchdown.

The Lions have been stringent about protocols since the start of training camp and have not had a player placed on the COVID-19 reserve list since the beginning of August. At that point, eight Lions players were placed on the COVID-19 reserve list in the first days after reporting for training camp, including Matthew Stafford, who had a false positive.

The NFL is testing all Tier 1 and Tier 2 employees for COVID-19 on a daily basis, including on game day. But Sills has said often that the league will not rely on testing alone.

"Just because someone has one negative test," Sills said, "we can't say that they're absolutely not infected."

Information from ESPN's Mike Rothstein was used in this report.