PHILADELPHIA >> If the NFL’s estimated $1 billion settlement of concussion claims isn’t approved, the league will pursue “scorched-earth litigation,” a lead lawyer for former players said Wednesday.

Christopher Seeger’s arguments opened a daylong “fairness hearing” on the plan in federal court in Philadelphia. The deal would settle thousands of lawsuits that accuse the NFL of long hiding what it knew about concussion risks to rush players back on the field.

“It would have been an expensive, scorched-earth litigation (without a settlement). We know that because of other parties that have litigated with the NFL,” Seeger said.

The NFL has deployed several strong legal defenses already. The league has said the dispute belongs in mediation under the contract; that former players can’t prove which concussion caused which injury; and that many ex-players filed suit too late. On the other hand, the NFL would have to open their files if the case goes to trial, and potentially disclose damaging information.

“What matters now is time, and many retired players do not have much left,” former Philadelphia Eagle Kevin Turner said in a statement Tuesday urging the plan’s passage.

Turner, at 45, has battled Lou Gehrig’s disease since 2010 and was too ill to attend the hearing.

The NFL expects about 6,000 former players to develop Alzheimer’s disease or moderate dementia in the coming decades. Their awards could reach $3 million, but would likely average $190,000, given reductions for advanced age, other medical conditions and years in the league.

Some critics feel that’s not enough to cover their needs, while others complain that there are no awards for depression, mood swings, dizziness and other problems they link to football concussions.

Another chief concern is that the plan leaves out future payments for chronic traumatic encephalopathy, or CTE, which some call the signature disease of football. The estates of players who died and were diagnosed with CTE from 2006 to 2014 can seek up to $4 million, but future deaths are excluded to avoid “incentivizing” suicide. The problem cannot currently be diagnosed in the living.

Thomas Demetrio, a lawyer representing the family of former Chicago Bears safety Dave Duerson, argued that CTE is “not going away.” Duerson, a fan favorite whose life derailed into increasingly erratic behavior, shot himself in the chest in a 2011 suicide. He left behind a note asking that his brain be tested for CTE. The tests were positive.

“The NFL by this settlement will never have to say what they knew, when they knew it, and CTE — Poof! It’s gone,” Demetrio argued.

Demetrio ridiculed the $112 million in legal fees the players’ lawyers could split, suggesting the only person who earned it was NFL lawyer Brad Karp.

Senior U.S. District Judge Anita Brody gave preliminary approval of the plan in July after the NFL lifted a proposed $765 million cap. The total includes $75 million for baseline testing and $10 million for research. With inflation and lawyer fees, the NFL could pay out $1 billion or more over 65 years.

The case involves only retirees who played under earlier contracts. About 200 retired players opted out and could sue on their own.

NFL widow Eleanor Perfetto of Annapolis, Maryland, is set to testify against the current plan on Wednesday afternoon. She has advanced degrees in health policy and statistics but finds the payout grid — men will get different amounts based on their diagnoses, how old they are and their NFL experience — baffling.

Her husband, Ralph Wenzel, suffered from dementia for more than a decade before he died in 2012. Tests showed he had both CTE and Alzheimer’s disease.

“An earlier diagnosis was prevented thanks to the NFL’s actions — exactly the actions the plaintiffs are suing for,” Perfetto wrote to the judge.