The NFL responded Tuesday night to the NFLPA's counterproposal on coronavirus-related reopening protocols, but a source told ESPN that some major issues remain unresolved, including a dispute over whether COVID-19 should be classified as a "non-football injury."

According to sources, the NFLPA has made several requests of the league, including daily COVID-19 testing, the elimination of all preseason games, financial and other compensation for players who opt out of playing for COVID-related reasons and a provision that would keep the 2021 salary cap from going down due to lost 2020 revenue.

But one source said Wednesday that a major sticking point is that the league's proposal so far would classify COVID-19 as a non-football injury. The players are pushing back on that, because when a team places a player on the Non-Football Injury list, it is not required to pay that player.

Hypothetically, if a player contracts the virus during a practice or a game and is placed on NFI as a result, his team would have the right not to pay him during his absence. Obviously, the NFLPA is fighting to avoid such a scenario.

Hovering over the discussions is the spike in coronavirus cases in states like Texas, Arizona and California and the increasing possibility that those states might soon be implementing shutdown provisions that would limit large gatherings. Should that happen, it's possible teams in those states wouldn't be able to hold training camps.

An earlier NFL-NFLPA agreement stipulates that teams this year are required to hold training camps at their own team facilities, and that if any team cannot open its facility, no team will be allowed to open its facility. For that reason, even though the league has insisted it plans to start training camps and the regular season on time, there remains a possibility that external circumstances could force a delay to the start of either or both.

As of early Wednesday afternoon, there were no more formal talks scheduled between the NFL and the NFLPA, though it's expected they will speak again soon. The NFLPA was holding an internal planning call Wednesday afternoon to discuss the NFL's latest proposal, and the union also was holding a previously scheduled call with player agents later Wednesday afternoon.

Information from ESPN's Jeremy Fowler was used in this report.