A federal appeals court has upheld the National Football League's estimated $US1 billion ($A1.31 billion) concussion settlement with former players, calling the agreement fair, if "not perfect".
A group of players had objected to the deal, which was approved in April 2015 by US District Judge Anita Brody in Philadelphia, because it did not cover potential victims of a degenerative brain diseases that scientists have linked to repeated blows to the head.
"It is the nature of a settlement that some will be dissatisfied with the ultimate result," Circuit Judge Thomas Ambro wrote for a three-judge panel of 3rd US Circuit Court of Appeals in Philadelphia.
"But they risk making the perfect the enemy of the good."
Representatives of the NFL, the objecting players and the retirees who signed on to the deal did not immediately respond to requests for comment.
The settlement calls for payments of up to $US5 million ($A6.5 million) each to former players diagnosed with certain neurological disorders, but it does not address chronic traumatic encephalopathy (CTE), which some researchers say can be caused by concussions.
The lawsuit was brought on behalf of more than 5,000 retired players, though the settlement could cover more than 21,000 former players, according to the court.
Roughly 200 retirees objected to the agreement, saying it did not account for players yet to be diagnosed with CTE.
They also argued the deal unfairly favoured currently injured retirees and left thousands of former players who have not yet been diagnosed with neurological diseases without a remedy.
CTE has been discovered during autopsies for several former players, including Hall of Fame linebacker Junior Seau and Pro Bowl safety Dave Duerson, who both committed suicide. In March, the NFL for the first time acknowledged a link between football and CTE.
But the appeals court noted that the research surrounding CTE is still nascent, with no current way to test for the disease while an individual is still alive. It also said many of the symptoms associated with CTE, such as memory loss, are eligible for compensation under the settlement.
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