Adam Schefter describes how optimistic the NFL and NFLPA are that the 2020 NFL season will start on time despite the coronavirus outbreak. (1:44)

How likely is it for the NFL season to start on time? (1:44)

Although the NFL remains hopeful of starting its regular season on time and in front of packed stadiums, its chief medical officer, Dr. Allen Sills, said Thursday that certain prerequisites -- including widespread testing for the coronavirus -- must be met for that to happen.

Sills' comments to NFL.com came two days after the league's general counsel, Jeff Pash, told reporters on a conference call that the "expectation" is to begin the regular season as scheduled in September.

Sills acknowledged that outcome is just one of many given the fluidity of the pandemic's effect and how the country continues to try to deal with it.

"I think what was implied there [by Pash] was to say we are not at a point where we are saying that is absolutely not going to happen so we should continue our planning and preparations as if we're going to be able to do that," Sills told NFL.com. "But obviously we're going to have to evaluate that along the way. And follow what the recommendations are from public health officials and from our infectious-disease experts and others."

Among the conditions Sills noted must be met for the NFL to begin practices and games on time is the availability of point-of-care coronavirus tests -- which yield quick results and can be done off-site from hospitals, for example -- and the removal of gathering restrictions due to the pandemic.

"As long as we're still in a place where when a single individual tests positive for the virus that you have to quarantine every single person who was in contact with them in any shape, form or fashion, then I don't think you can begin to think about reopening a team sport," Sills told NFL.com. "Because we're going to have positive cases for a very long time."

Football has been the one major sport whose calendar has been unaffected by the coronavirus due to the fact that it takes place in the fall. Others such as basketball, baseball and hockey have been put on hold for the immediate future.

Sills said the NFL won't act in a vacuum when it decides on how it will handle playing games and noted there's no current timeline for when that decision must be made.

"We will make those decisions in consultation with our experts at the time," Sills said. "That decision will not be made in isolation. The NFL will not be charting a course different than other professional sports, other parts of society -- college sports, universities, businesses."