The report published Saturday said Rivera gave players likely scenarios that could impact the team if players were out with COVID-19 during the season.
The report also says Rivera spoke with some players about their hesitation over getting the vaccine and helped set up appointments for others.
According to a July 30 report from the Associated Press, 88.5% of NFL players have had at least one shot of the vaccine and 20 teams have more than 90% of players vaccinated, including eight with more than 95% vaccinated.
The league can't mandate the vaccine but it made its stance clear through strict protocols for players who don't get it. Teams are required to make unvaccinated players visually identifiable and the league recommended use of colored wristbands or credentials.
Teams that experience a COVID-19 outbreak among unvaccinated players could forfeit regular-season games, with players on both teams not getting paid.
The Indianapolis Colts and Washington were the last two teams to surpass 50% vaccination rates.
The Associated Press contributed to this report