The NFL's chief medical officer, Dr. Allen Sills, has come out against shifting to a bubble environment amid the league's run of positive COVID-19 test results.

Sills doesn't believe a bubble would be foolproof and is wary of the mental health risks of an extended period of social isolation.

He added that the league hasn't ruled out the option of a bubble later this season.

The NFL has rescheduled nearly a dozen games through Week 5 and had a total of 47 confirmed infections across the league during the past two testing periods.

"I think we all have to recognize that there are no perfect [solutions] here," Sills said. "First of all, a bubble is not going to keep out all infections. You still have other individuals that come in and out: service workers, security, other personnel. And we've known from other experiences that those individuals can be infected. So simply being in a bubble doesn't keep us safe. We still have to do all these measures of mitigation, with PPE, with identifications of symptoms, with testing, etc."