Ten retired NFL players, including former Washington Redskins running back Clinton Portis, are accused of defrauding a league health care program by submitting fake invoices for medical equipment, including a hyperbaric chamber, which they never actually purchased, federal prosecutors said Thursday.

The retired players got $3.4 million in fraudulently gained reimbursements from a fund that reimburses former NFL athletes for out-of-pocket health care expenses, prosecutors said.

"A group of former players brazenly defrauded the plan by seeking reimbursements for ... expensive medical equipment that they never purchased," Assistant Attorney General Brian Benczkowski told reporters in Washington D.C.

"Things like hyperbaric oxygen chambers, ultrasound machines used by doctors' offices to conduct women's health exams, and even electromagnetic therapy devices designed for use on horses."

The players submitted forms for $3.9 million in reimbursements and received $3.4 million between June 2017 and December 2018, officials said.

Ring leaders recruited other former players to participate in the scheme and got thousands of dollars in kickbacks once reimbursement checks were received, prosecutors said.

The plan's administrators, Cigna, spotted the irregular claims and reached out to federal authorities, officials said.

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"In each case, the forms submitted in support of the claims were completely fabricated," Benczkowski said. "These included things fake invoices from medical supply companies and forged letters and prescriptions from medical care providers."

The phony reimbursement claims generally ranged between $40,000 and $50,000, according to Benczkowski.

"By defrauding the plan and treating it like their own personal ATM, sadly the defendants placed the plan's tax-exempt status at risk and threatened the ability of law-abiding former players to continue to receive tax-free reimbursement for legitimate medical expenses for themselves or their families."

The plan is for former players, so no current players are part of this investigation, according to prosecutors.

In addition to Portis, other former players accused of fraud include cornerback Carlos Rogers, linebacker Robert McCune, cornerback John Eubanks, wide receiver Tamarick Vanover, cornerback Ceandris Brown, safety James Butler, safety Etric Pruitt, cornerback Fredrick Bennett and running back Correll Buckhalter.

McCune, who played in eight games in fives seasons with the Redskins, Baltimore Ravens and Miami Dolphins, was allegedly the first defendant to file a false claim in 2017, according to a grand jury indictment.

The 40-year-old McCune, who lives in Riverdale, Georgia, did not immediately return messages, left at his listed phone numbers and email addresses, seeking his comment on Thursday.

The 38-year-old Portis was the best known former player among those charged by the Justice Department. Portis played nine seasons in the NFL, from 2002 through 2010, and rushed for more than 1,000 yards in six of those years.

Portis has struggled in his post-playing life, having filed for bankruptcy in 2015. The retired running back once told Sports Illustrated magazine that he considered murdering the men he believed mismanaged his $43.1 million in career earnings.

Portis’ attorney, Mark Dycio, said his client only referred players to the plan and did nothing wrong.

“Mr. Portis believed to be participating in a health care program sanctioned by the NFL,” Dycio told NBC News shortly after the charges were announced. “He’s completely taken aback by the indictment and looks forward to clearing his name.”

Federal prosecutors also plan to file charges against wide receivers Joe Horn and Donald "Reche" Caldwell, authorities said.

The players were charged with multiple counts of wire fraud, conspiracy to commit wire fraud and health care fraud. They face up to 20 years behind bars and fines up to $250,000 if convicted on all charges, prosecutors said.

The fund that was allegedly raided is "The Gene Upshaw NFL Player Health Reimbursement Account Plan," which was created in 2006 by the league's collective bargaining agreement with the union. It provides tax-free reimbursement of out-of-pocket costs to eligible former players, their spouses and dependents.