When the novel coronavirus pandemic forced the shutdown of sports in mid-March, it appeared as if the NFL had time on its side. It conducted its offseason business remotely, with the hope and assumption that its plans for an uninterrupted season would be bolstered by an ever-improving national response to the outbreak.

But with caseloads elevated in many parts of the country and the return of major league baseball already threatened by a string of positive tests, time has turned out to be the NFL’s foe.

“I’m not sure there was any more implicit assumption than that we all thought [in early discussions of health protocols] that things would trend in a more positive direction,” DeMaurice Smith, the executive director of the NFL Players Association, said in a recent video conference with reporters. “The reality is in a lot of states right now, that trend has been in an opposite direction.”

The NFL pushed forward this week, with teams opening training camps, but its aspirations for an unaltered season were dented by an increasingly foreboding set of circumstances. Some players are opting out of the season. New Orleans Saints Coach Sean Payton told reporters Wednesday, “There’ll be some suspended games.” Allen Sills, the league’s chief medical officer, said in a phone interview Monday he remained “cautiously optimistic” about the season but recognized “this is going to be hard.” Players and coaches are being asked whether they think a full season is possible.

“I can’t call it,” Baltimore Ravens quarterback Lamar Jackson, the reigning league MVP, said in a midweek video conference. “I feel here, I just know what we have going on in this building, we’re doing a pretty good job. We’ve got our [trackers] on, making sure we’re all staying safely apart from each other. We’ve got our hand sanitizer. … We’ve got our masks on throughout the building, and no one that I know of has covid-19 [the disease caused by the coronavirus]. I feel like we’ve been doing a pretty good job. I can’t speak for everyone else. I hope we can finish the season, though.”

Jackson called himself “the new bubble boy.” But while sports such as the NBA, the NHL and MLS are operating successfully with players gathered at one or two sites and isolated from the outside world in bubble environments, the NFL’s model is more like MLB’s, with teams playing in their home cities and their own stadiums. Baseball’s ongoing issues, primarily surrounding the Miami Marlins, are ominous.

“If you see that kind of outbreak in Major League Baseball,” said Zachary O. Binney, an epidemiologist at Oxford College of Emory University, “I would expect the NFL to have a more difficult time because you have more people and more contact. … They’re trying to do essentially what MLB has done. And unless you believe that your people are going to be that much more responsible or your protocols are that much better, I’m afraid you’re going to see the same scenario.”

Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases, told CNN in mid-June that “football may not happen this year” without players in a bubble. But while Sills said Monday that “we absolutely have to remain flexible about everything we’re doing,” a bubble setup that has teams gathered at a single site or a small number of sites has not appealed to the NFL or NFLPA — in part because of the number of players, coaches and staffers who would be involved, the amount of space that would be required and the length of the full season ahead.

Binney said he wants to see the NFL play and suggests teams might be able to use “home-market bubbles” with players, coaches and staffers isolated from their communities in selected hotels.

“This all goes back to the fact we haven’t gotten the virus under control [in the United States], and that makes it more difficult to take steps toward normality,” Binney said in a phone interview.

The NFL has set up what it regards as a mini-bubble at each team’s facility, with strict protocols in effect but with players, coaches and staffers going home at day’s end. Players are to be tested daily for at least the first two weeks of training camp, with a possible switch to every other day thereafter based on the rate of positive tests. Players, coaches and staffers wear tracking devices within teams’ facilities to assist with distancing measures and contact tracing. Players can be disciplined for engaging in any high-risk behavior that threatens to spread the virus while they are away from team facilities. A player must test negative three times after reporting to camp just to be allowed inside the facility.

“This is all of us in it together,” Cleveland Browns center JC Tretter, the union’s president, said during the recent NFLPA video conference. “So about doing the right thing — everybody in that community, everybody in that facility has to do the right thing.”

The NFL has said it expects to receive testing results within 24 hours. That still might allow time for an asymptomatic carrier to unwittingly expose others within a facility before a positive test result is known. Other safety measures would have to compensate.

“If you look at things that are going on in our world right now,” Ravens Coach John Harbaugh said Thursday, “and our country in terms of the new normal, in terms of the way we live and deal with this stuff, whether it’s grocery shopping or how we get gas and all that, you’ve got to figure it out and find a way to do things a little bit differently.”

If total buy-in by all participants is required, the NFL may be hard-pressed to avoid the divisions affecting the response of the country as a whole. Carolina Panthers tackle Russell Okung wrote Wednesday on Twitter: “I’ve never cared less about scientist recommendations than now, they are the new politicians.”

The economic agreement struck between the league and NFLPA reflects the possibility of the season being canceled. The NFL’s competition committee and the league office’s football operations department are studying scenarios by which teams could be shut down, an entire week of regular season games could be postponed or play could be halted.

“We don’t believe that the right way of looking at this is somehow bending covid to football,” Smith said. “We’ve got to bend football to the virus.”

NFL Commissioner Roger Goodell wrote Monday in a letter to fans that the league and NFLPA hope to have “a healthy and complete 2020 season.” Around the league, fingers are crossed.

“Every decision we make this year needs to be made through a medical lens of what’s the safest and healthiest way to move forward,” Tretter said. “So as we look through all of these issues, the only way we’re going to be able to make it through a full season is if that’s the criteria on which we make our decisions.”