A Minnesota federal judge on Friday blocked former National Hockey League players from bringing as a class action claims that the league ignored scientific evidence that head trauma in sports can cause long-term brain diseases, dealing a major blow to the players and potentially to other athletes bringing similar claims against their former leagues.

Instead of forcing the NHL to face classes of more than 5,000 former players and their families over the question of whether the league knew or should have known of this growing body of scientific evidence, the players may now have to bring claims on a case-by-case basis, a process experts say will be more costly and difficult and make it unrealistic for many players to pursue.

This outcome, though not an end to claims against the NHL, stands in stark contrast to similar claims against the National Football League, which agreed to an unmapped class settlement that could pay out more than $1 billion to former players suffering from brain diseases.

"I'd say this denial of class cert is a monumental setback for the players, especially compared to the success of players in the similar NFL and NCAA cases," said Jenner & Block LLP partner Michael J. Nelson, a sports and commercial litigator who defended a high school concussion class action.

"Now they are going to have to go presumably player-by-player proving damages," Nelson said. "That is where the NHL's leverage comes in because some low-dollar cases might be so weak that the players give up and those cases may never see the light of day, and the higher dollar cases will still be drawn out over a period of years."

The ruling further allows the NHL to avoid what could have been a costly payout for medical monitoring of retired players, something that might have uncovered more players with serious brain diseases and disorders.

"From a strategic standpoint, they obviously did not want this to be certified because then it is a potentially very, very expensive remedy that is available to the class," said mass tort litigator Timothy O'Brien of Levin Papantonio Thomas Mitchell Rafferty & Proctor PA. "So I am sure that the NHL perceives itself to have dodged a bullet on this."

The players had sought to bring a class action containing two classes, one for players or the families of those players who have been diagnosed with certain neurological diseases or disorders, such as a host

of brain diseases and disorders like dementia, Alzheimer's and chronic traumatic encephalopathy, or CTE, and another for living retired players who may manifest such problems.

They wanted the league to be forced to pay for medical monitoring to allow players to get screened and perhaps receive preventative treatment.

The problem for U.S. District Judge Susan Richard Nelson, however, was that medical monitoring required substantive questions that would turn on varying state laws depending on where the player lived or played. Many states do not even recognize medical monitoring, she said.

"Given those differences, the court finds that resolving these claims in a single class action would present significant case management difficulties," the judge said.

O'Brien said that obtaining class certification on medical monitoring claims in a nationwide class action like this without a settlement is tough.

Concussion and head injury claims in other sports have resulted in major settlements, most notably with the NFL. A similar concussion case against the NCAA resulted in a nationwide medical monitoring settlement, though final approval has been delayed, while personal injury claims continue.

The judge's ruling in the NHL case may show that medical monitoring is no longer a viable option, removing a "play out of the plaintiffs' playbook," Michael Nelson said.

However, the ruling does not dispose of all the personal injury claims the former players can pursue against the league, and attorneys for the players said they will continue to pursue those claims while examining whether to seek an appeal.

"We will continue to litigate the players' claims on a case-by-case basis for all who have incurred injuries and damages," Charles S. Zimmerman of Zimmerman Reed LLP, one of the players' attorneys, told Law360 on Monday. "Players with traumatic brain injuries need to file their claims and justice will prevail as we move forward."

But proceeding on an individual basis has its challenges, something the judge acknowledged, noting the "court is sympathetic to the significant cost and likelihood of duplicative proof in trying this case many times, for each individual player."

Just last month, an Illinois federal judge put an end to the case brought by the parents of deceased NHL player Derek Boogaard, who was posthumously diagnosed with CTE.

While the decision turned on the fact that the Boogaards were not named as trustees for a wrongful death action under state law requirements, the judge, in that case, went on to suggest that they had not properly pled the league was negligent because it did not properly disclose the risks of head injuries.

The former NHL players who had sought to pursue the class action will now have to wade into these murky waters.

"There is a lot of leverage in the numbers of a class and now those numbers are gone and the leverage has flipped to the NHL," Michael Nelson said. "Time heavily favors the NHL and it can now take its time with these cases one-by-one."

The case is In re: National Hockey League Players' Concussion Injury Litigation, case number 0:14-md02551, in the U.S. District Court for the District of Minnesota. 

This article was first published in Law360.