PHILADELPHIA >> A federal judge has ordered the NFL and former players to negotiate over whether claims of concussion-related injuries will move forward in court or in arbitration.

U.S. District Judge Anita B. Brody of Philadelphia had planned to rule July 22 in a legal fight involving about 4,200 former players and the league.

However, in an order Monday, she told the two sides to try and resolve how the case will proceed by going through mediation with retired U.S. District Judge Layn Phillips of Oklahoma. The retirees want the right to sue the league, while the NFL insists the claims fall under the collective bargaining agreement, and should be resolved in arbitration.

“We respect and will comply with the court’s order regarding mediation and will be available to meet with Judge Phillips at his direction,” NFL spokesman Greg Aiello said in a statement.

Phillips is to report back to Brody on any progress by Sept. 3. Brody also implemented a gag order on lawyers for both sides.

Many former players say they suffer from dementia, Alzheimer’s disease and other neurological conditions and believe they stem from on-field concussions. The league says safety has always been a top priority.

Each side hired a powerful Washington litigator to make its case to Brody during arguments in April.

NFL lawyer Paul Clement argued that teams bear the chief responsibility for health and safety under the contract, along with the players’ union and the players themselves.

“The clubs are the ones who had doctors on the sidelines who had primary responsibility for sending players back into the game,” Clement said after the hearing.

The players argued that the league glorified violence through NFL Films, thereby profiting from dangerous hits to the head.

Players’ lawyer David Frederick also accused the league of concealing studies linking concussions to neurological problems for decades, in part by hiring a rheumatologist to lead the Mild Traumatic Brain Injury Committee, which was created in 1994.

“It set up a sham committee designed to get information about neurological risks, but in fact spread misinformation,” Frederick argued.

In recent years, a string of former NFL players and other concussed athletes have been diagnosed after their deaths with chronic traumatic encephalopathy, or CTE, including popular Pro Bowler Junior Seau and lead plaintiff Ray Easterling. Both committed suicide last year.

About one-third of the league’s 12,000 former players have joined the litigation since Easterling’s suit was filed in 2011.

Brody, during the oral arguments, pondered whether NFL head injuries belong in arbitration under terms of the contract.

“It has to be really specific,” she said. “That’s what I have to wrestle with.”