Millen, 60, suffers from amyloidosis, he told The Morning Call of Allentown, Pennsylvania. The disease occurs when amyloid builds up in bone marrow and then ends up in tissue or organs. As the disease progresses, the protein can alter the healthy tissue it is near, causing organ failure.

In Millen, the disease is attacking his heart, according to the newspaper, and symptoms generally aren't obvious at first.

According to The Morning Call, Millen's heart is working at about 30 percent of capacity, and he is believed to eventually need a heart transplant. To help in treatment, Millen has been having chemotherapy once a week for the past eight months. Chemotherapy is believed to halt the abnormal cell growth.

Millen, a former ESPN employee who still is an analyst for Big Ten Network, first began having symptoms of the disease seven years ago when he had chest pain during exercise. He went for tests over the next six years without a diagnosis, before the Mayo Clinic in Jacksonville, Florida, diagnosed amyloidosis last summer.

"I know what you have, and you're not going to like it," Millen said the doctors told him, according to The Morning Call. Millen continued to work games last season for BTN.

Millen was drafted in the second round out of Penn State in 1980 and played 12 seasons at linebacker in the NFL for the Raiders, San Francisco 49ers and Washington Redskins. He made the Pro Bowl once, was an All-Pro twice and won four Super Bowls.

After his NFL career, Millen became a color commentator on NFL games before being hired by the Lions in 2001 as the team's president and general manager. He held that role for seven-plus seasons before being fired early in the 2008 season, when the Lions went 0-16.

Millen, according to The Morning Call, appears to be taking his diagnosis with a level of positivity, still mowing his lawn and woodworking in his Pennsylvania home.

"I've always lived this way," Millen told the newspaper. "You take what you get. I look over my life, and it's been a storybook. I have an awesome family, a phenomenal wife, and you can't ask for more.

"So you're not supposed to take the good with the bad? When a bump comes up in the road, you deal with it. It's ridiculous to feel sorry for yourself. I'm thankful for what I have, and I'll take what I get."

While amyloidosis can affect anyone, 70 percent of those diagnosed with the disease are men, according to the Mayo Clinic. Of those, many are between the ages of 60 and 70.