Participants on a board of governors call on Tuesday with NBA commissioner Adam Silver left the virtual meeting feeling increasingly positive about the league's momentum toward a resumption of play this season, sources told ESPN.

Owners and executives on the call were encouraged about the league's progress toward minimizing health risk upon a return and the league office's positive conversations with the National Basketball Players Association about the players' desire to eventually restart the season, sources said.

Discussions centered on health and safety concerns, including the goal of getting team officials and players comfortable with the idea that a positive test for the coronavirus upon a return would not shutter play.

Silver told those on the call that if a positive test would "shut us down, we probably shouldn't go down this path."

The question remains: How many positive tests would be too many? That is among the questions that the NBA, NBPA and medical experts have to come to terms with in the coming weeks before the league and union can greenlight a resumption of play.

Once the NBA formalizes a return to play, the league indicated to teams that the plan would be to standardize coronavirus testing among the 30 teams, sources said. For now, the NBA is allowing teams to use a variety of tests.

As for the format in a return to play, there still is no decision on the kind of form that would take with the 30 NBA teams, sources said. The league hasn't worked through the details on whether all 30 teams would return or whether regular-season games would be played or if perhaps there would be a play-in tournament to give more teams a chance to make the 16-team playoff field, sources said.

When asked about the bubble-isolation plan on the call, Silver described it as a "campus environment," sources said. He has talked about one or two locations for players, and the focus continues to be on Orlando's Walt Disney World Resort and Las Vegas, sources said.

The NBA shared with owners several factors that it plans to study over the next two to four weeks before deciding on restarting the league.

Among them, sources said: Understanding the trajectory of new cases in those states starting to reopen, understanding who is getting severely ill and why, and developments in testing types. The NBA also is studying how other leagues are handling positive tests among participants, sources said.

On the call, the league office wasn't optimistic about rapid-response testing becoming widely available within the next month, sources said.

There was growing confidence among owners on the call about how players were responding to the return to practice facilities. The league believes it will have 22 of its 30 facilities open by Monday, sources said.

The league office described to owners how leagues in the United States -- and across the world -- are handling a return to play, especially detailing overseas leagues, from the Premier League to La Liga to the Chinese Basketball Association, sources said.