ST. PAUL, Minn. — The federal judge overseeing the NHL concussion case has denied class-action status for the former players suing the league over head injuries.

U.S. District Judge Susan Richard Nelson issued her 46-page order on Friday, the first significant victory for the league in a landmark lawsuit that was filed almost five years ago.

Nelson wrote that “widespread differences” in state laws about medical monitoring, which the retired players are seeking, would “present significant case management difficulties.”

The judge declined to certify either of the proposed classes by the ex-players. They sought to create one group of all living former NHL players and one group of all retired players diagnosed with a neurological disease, disorder or condition. More than 5,000 former players would have been allowed to join the case.

The last hearing on the class-action status was held in March.

More than 100 former players have added their names to the case. The retirees have accused the NHL of failing to better prevent head trauma or warn players of risks while promoting violent play.

An attorney for the players, Charles Zimmerman, said the judge’s ruling was procedural, and that hundreds of players are prepared to try their cases individually.