The judge presiding in the proposed $765 million settlement between the N.F.L. and more than 4,500 retired players who sued the league and accused it of hiding the dangers of concussions has raised significant questions about whether there will be enough money to pay for all of the payouts, medical tests and treatment. Judge Anita B. Brody of the United States District Court for the Eastern District of Pennsylvania rejected the proposed settlement because the league and the plaintiffs’ lawyers had not produced enough evidence to persuade her that $765 million would cover the potential costs for 18,000 retirees over the 65-year life of the agreement. “I am primarily concerned that not all retired N.F.L. football players who ultimately receive a qualifying diagnosis or their related claimants will be paid,” Brody wrote.

The lawyers for the players have said that economists and actuaries have said there will be sufficient money available.

“Unfortunately, no such analyses were provided to me in support of the plaintiffs’ motion,” Brody said. “In the absence of additional supporting evidence, I have concerns about the fairness, reasonableness and adequacy of the settlement.”

The judge’s ruling will probably force the plaintiffs’ lawyers and the N.F.L. to provide documents proving that there will be enough money to pay for the retired players’ claims. If the judge remains unconvinced, the league and the lawyers could increase the size of the settlement, change the amount of the payouts or limit who might be eligible. Even if the league and the lawyers for the players convince the judge that there will be enough money to go around, her ruling on Tuesday will undoubtedly delay when players may get paid. The proposed settlement that the judge reviewed, which was released last week, was to form the basis for mailings sent to retired players. The players would then have several months to approve the settlement, or opt out of it.

None of this means the settlement is off, however. There are tweaks that can be made and, as Christopher Seeger, co-lead counsel for the plaintiffs said in a statement, “analysis from economists, acutaries and medical experts” will prove that the settlement will take care of the players in question.

“We are confident that the settlement will be approved after the Court conducts its due diligence on the fairness and adequacy of the proposed agreement,” Christopher Seeger, co-lead counsel for the plaintiffs, said in a statement. “Analysis from economists, actuaries and medical experts will confirm that the programs established by the settlement will be sufficiently funded to meet their obligations for all eligible retired players. We look forward to working with the Court and Special Master to address their concerns, as they rightfully ensure all class members are protected.

“We believe this is an extraordinary settlement for retired NFL players and their families, and have received overwhelming support as they have learned about its benefits. We look forward to finalizing this agreement so they can soon begin taking advantage of its benefits.”

Florida-based lawyer Sia Nejad, who specializes in insurance defense, says this rejection is a matter of wanting the NFL to “show its work.” “At this point, it seems that Judge Brody is doubting that the $765 million is sufficient to cover the players and that some of the parameters to qualify for portions of the settlement monies are too narrow or restrictive. Bottom line, she wants the lawyers to ‘show their work’ because she’s doubting the fairness of the agreement.”