One tabloid is claiming that incarcerated football legend O.J. Simpson has morphed into what they describe as a “walking heart attack.”

The National Enquirer says sources tell them that Simpson has packed on 50 pounds, sparking fears among friends and family members that he is in danger of cardiac arrest behind bars.

The source describes O.J., who is is currently serving time at the Lovelock Correctional Center near Reno, Nevada, as “turning into a butterball,” adding, "If he doesn't go on a diet, he's going to die of a massive heart attack in jail. His kids are worried about him."

The Enquirer claims that while Simpson is “depressed over his weight,” he feels powerless.

The source quotes the ex-football star as saying, “I'm a heart attack waiting to happen. When I leave here, they'll probably be taking me out in a pine box.”

O.J. Simpson was sentenced to up to 33 years on charges of kidnapping, armed robbery and assault with a deadly weapon, stemming from a 2007 confrontation over sports memorabilia. His request for a new trial was denied last October.

(Photo: Jae C. Hong-Pool/Getty Images)