When the N.F.L. agreed to pay $765 million to settle a lawsuit brought by 4,500 retired players who said the league hid from them the long-term impact of concussions, lawyers in the case said all retirees would be eligible for a share of the settlement.

The number of former players eligible to receive payments, though, may be relatively small. Only players with the most severe brain injuries would be compensated, and the estates of retirees who died before 2006 would be excluded, according to a confidential letter that outlined some of the components of the proposed settlement sent on Oct. 9 to players represented by Hausfeld, one of the law firms that sued the N.F.L.

Players found with a severe brain injury after they turned 45, or who played in the N.F.L. for five years or less, would probably receive smaller payouts, the Hausfeld letter said.

The details of the settlement, which requires approval from Judge Anita B. Brody of United States District Court for the Eastern District of Pennsylvania in a fairness hearing in the coming weeks, may disappoint some players who hoped to be paid. After the deal was announced in late August, some retired players said they felt the settlement was too small. Others were angry that their lawyers would not be able to learn more about what the N.F.L. knew about the dangers of concussions. The league did not admit to any fault in the settlement.