An outbreak of COVID-19 among players who have not been vaccinated against the disease could cause financial losses and forfeits without pay, the National Football League announced on Thursday.

The announcement was made by Roger Goodell, the commissioner of the NFL, in a memo that urged the participating players to get vaccinated against the deadly disease. The memo, however, fails to mandate the policy for teams.

NFL teams began pre-season training camps this week with the 2021 campaign set to start in September.

Under terms established in the memo, if a team has a COVID-19 outbreak and a game cannot be played or rescheduled during the 18-week season, the team with the outbreak will forfeit the contest.

The team responsible for an unplayed game due to unvaccinated players or staff will be responsible for covering financial losses for the canceled game and possible discipline for the commisioner.

That move essentially pressures teams to get their personnel vaccinated as the potential expenses for an unplayed game, from ticket refunds to lost league telecast revenue, could be steep.

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There will also be peer pressure from teammates as well as players on other teams, who risk losing their paychecks from a game because a rival club has an outbreak and forfeits.

The memo released by the NFL states that all 272 games will be played in a span of 18 weeks, leaving no room for any rescheduling of the matches. It read, "We do not anticipate adding a '19th week' to accommodate games that cannot be rescheduled within the current 18 weeks of the regular season", according to reports from AFP.

The moves should avoid the major rescheduling issues COVID-19 produced last season, games being played on every day of the week and teams juggling plans to complete the season, AFP reported.

The memo also sets apart different treatments for those test who positive for COVID, depending on their vaccination status. Those who have received the shot will be allowed to resume activities after two negative tests that are taken at a gap of 24 hours if the infected person does not demonstrate any symptoms.

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However, in case the individual has not been vaccinated against COVID, they will be subject to isolation for at least 10 days.

"We will seek to minimize the burden on the opposing club or clubs. If a club cannot play due to a COVID spike in vaccinated individuals, we will attempt to minimize the competitive and economic burden on both participating teams."

The NFL also said that a new set of regulations are being drafted for the new season by the United States Centres for Disease Control and Prevention, according to reports from AFP.

According to the NFL Network, more than 78% of NFL players have had at least one shot of a vaccine and 14 teams have at least 85% of players vaccinated.

"We can play a full season if we maintain a firm commitment to adhering to our health and safety protocols and to making needed adjustments in response to changing conditions," the memo said, according to reports from AFP.

It added, "These operating principles are designed to allow us to play a full season in a safe and responsible way and address possible competitive or financial issues fairly."