The NFL has informed teams that the 2021 salary cap will be no lower than $180 million, a slight increase from last year's previous agreement between the league and the NFL Players Association.

The league told teams in a memo Thursday morning that $180 million is not the final 2021 cap figure, just an adjustment of the cap "floor" established last summer in negotiations between the NFL and the NFLPA.

The final 2021 cap figure, the memo says, "will be set following review of the final 2020 revenue figure and other audit and accounting adjustments." The new league year and free agency are scheduled to begin March 17.

Sources familiar with the negotiations told ESPN that the final number is likely to be between $180 million and $185 million, though almost certainly on the lower end of that range.

"As you know, one aspect of the agreements negotiated last summer with the NFLPA to address operations during the pandemic provides that the 2021 Salary Cap will be no less than $175 million," the memo said. "Following discussions with the union that addressed both actual 2020 revenues and projected attendance for the 2021 season, we have agreed to increase the minimum Salary Cap for the 2021 League Year to $180 million. We will promptly advise all clubs as soon as the Salary Cap is set."

Last summer, while negotiating the terms under which the league would proceed during the COVID-19 pandemic, the NFL and the NFLPA agreed to that original salary cap floor of $175 million per team for 2021. This was to guard against revenue losses sending the cap even lower.

One source said Thursday that the revenue numbers on which the cap is annually based would have led to a salary cap of roughly $160 million per team, which would have been a disastrously large drop from the $198.2 million cap under which teams operated in 2020.

With the floor now set at $180 million, the cap will be roughly $20 million higher than it would have been otherwise. That $20 million or so will have to be "borrowed" against future caps, and the manner in which that will happen is a subject of ongoing negotiations between the league and its players union.

To use a rough example: If revenue projections deliver a $220 million salary cap in 2022 and a $230 million cap in 2023, the sides could agree to reduce those numbers by $10 million each of those two years to make up for this year's $20 million discrepancy.

The final 2021 cap figure could take some time to finalize, as the NFL continues to negotiate new contracts with its TV network partners. New TV contracts would obviously affect revenue projections and could lead to an expansion of the NFL regular season to 17 games as early as this year.

But one source close to the talks said the best-case outcome of those negotiations still likely wouldn't raise this year's cap beyond about $185 million.

Teams are allowed to roll over cap room from previous years, so any extra room teams had under 2020's $198.2 million salary cap can be applied to 2021's cap.

Total attendance this past season was 1.2 million, down from 17 million in 2019. Thirteen teams didn't allow fans in the regular season; other clubs limited crowd size to provide social distancing in compliance with health and safety regulations in their state.

The Associated Press contributed to this report.