As some NFL players expressed wariness about participating in the 2020 season amid the coronavirus pandemic, their union and the league were attempting to work out the details by which they would prepare to play and the rules by which they could choose to sit out.

The NFL Players Association is seeking to have no preseason games this year, according to people familiar with the deliberations. The league so far has not appeared willing to budge from its recently reworked plan for a two-game preseason ahead of a regular season that begins Sept. 10.

The NFL and NFLPA also are working on guidelines that would govern how individual players could opt out of the season, according to people with knowledge of the discussions.

Thom Mayer, the NFLPA's medical director, and Allen Sills, the NFL's chief medical officer, addressed players during a conference call Friday. Players asked questions about the medical protocols being developed by the league and union. Some expressed concerns, according to multiple people familiar with the call.

The NFLPA has begun to prepare for the possibility that some players will choose to sit out the season, as has been the case in Major League Baseball and the NBA. The league and union must decide how such opt-outs would be handled contractually. Those discussions are underway.

For those who choose to play, the length of the preseason will be an issue. The league decided Wednesday to cut the preseason from four to two games per team. The first and fourth weeks of the original preseason schedule would be dropped, and each team would play one home game and one road game.

But the NFLPA seems to have reservations about players being exposed to coronavirus-related risks for essentially meaningless games. The union's preference for no preseason games was reaffirmed during a Thursday conference call with team player representatives.