The NFL has added an additional COVID-19 vaccination incentive for players, threatening forfeits and the loss of game checks if an outbreak among unvaccinated players causes an unresolvable disruption in the regular-season schedule.

Commissioner Roger Goodell informed clubs of the new policy Thursday in a memo. The league has encouraged vaccination for players but has not required it, per an agreement with the NFL Players Association.

Instead, the league has set up a series of incentives. As of Thursday, Goodell wrote, more than 75% of NFL players were at least partially vaccinated and more than half of the league's teams have player vaccination rates above 80%.

Unvaccinated players will be subject to severe protocols during training camp and the regular season, including daily testing, mask-wearing and travel restrictions. Thursday's memo made it clear that unvaccinated players could, in theory, be responsible for the losses of games and paychecks as well.