Incarcerated O.J. Simpson is living in fear behind bars because he's convinced his cellmate is plotting to kill him.

The former NFL star was sentenced to serve at least 15 years in a Nevada prison last December after his conviction for armed robbery relating to a September 2007 sports memorabilia heist.

He is serving his time at Lovelock Correctional Center as he awaits progress on his appeal, but according to the National Enquirer, Simpson is terrified his cellmate is plotting to take revenge on him for the murder of his ex-wife Nicole Simpson-Brown.

The retired sportsman was cleared of killing his ex and her friend Ron Goldman in 1995, but the shamed star is allegedly fearful he will become the target of a revenge attack.

According to the tabloid, Simpson has told pals, "My cellmate is nuts. He's a killer, and he hates me. He told me that he is in prison for murder and rape, and he hates my guts because I got away with murdering my ex-wife.

"He's told me he is going to strangle me in my sleep the first chance he gets."

Friends of Simpson are worried The Naked Gun star is gradually being driven to insanity and are concerned he will not survive his prison stint.

An insider says, "I think O.J. is finally losing it. If he has to stay in prison for a long time, he won't make it."

Simpson is due back in court on August 3 when a judge will decide whether to grant him bail pending his appeal.

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(This news article provided by World Entertainment News Network)