Players from 15 NFL teams including the Jets have stated they will not participate in Voluntary Workouts, scheduled to start next week, due to concerns over the COVID-19 pandemic. https://www.nytimes.com/2021/04/16/sports/football/nfl-covid-voluntary-workouts.html
It's a logical response from a pissed off player base that really doesn't want to play 17 games and that still has major doubts about whether the NFL is taking Covid-19 safety seriously. The new wave of Covid-19 is beginning to effect the 24-39 demographic fairly heavily. Lots of long Covid there although nothing like the death rate of last year, maybe 10% of that.
The problem for the players is they have consistently lobbied for less and less practice time so it’s hard to take seriously the idea that this is for health/covid concerns.