National health concerns have changed the way NFL teams are doing contracts for free agency -- and some players won't be happy about it.

Because teams are unable to oversee physicals due to the coronavirus outbreak, they have added provisions in player contracts stating that failed physicals will result in forfeited signing bonus money, league sources told ESPN.

The problem is that some players might not get a physical for months because of travel logistics related to the coronavirus, which has caused teams to shut down their operations for an indefinite period.

"Clubs are permitted to expressly condition a free agent's eligibility to receive and retain bonuses or an injury guarantee upon the player being given and passing a physical examination by the club's medical doctor when travel restrictions are lifted," a league official said.

If a player signs a three-year, $30 million contract with a $10 million signing bonus this week, for example, but fails a physical in June, he could lose the $10 million and be bound to a three-year, $20 million deal, potentially.

It's uncertain how many teams are drawing this hard line, but several sources have encountered the provision when finalizing contracts over the past two days. These items are negotiable between the player and the team, to be sure, but one source said the NFL and NFL Players Association should create standard contract language fairly addressing the issue for both parties, because each team makes its own tweaks.

In a typical NFL year, a physical is necessary to consummate a deal. This year, many players are signing the deals and hoping for the best.

The NFL is giving teams the option to conduct a physical with an independent doctor. This is the case with Tom Brady and the Tampa Bay Buccaneers, who, according to ESPN's Jeff Darlington, are organizing a physical in the New York area where Brady lives.

Teams are trying to adjust to a vastly different free agency than in years past. When the league year started at 4 p.m. ET Wednesday, teams were not allowed to announce contract agreements until a player had signed a contract and passed a physical.

But on Thursday, the NFL told teams that it is now allowing transactions to be announced if (A) the team and player agree to terms of a contract, or (B) a written contract has been sent to a player and agent.