MICHAEL DOUGLAS is terrified that his druggie will never get out of prison alive!

The legendary actor revealed his secret torment to pals after learning that Cameron – who’s locked up at a Pennsylvania correctional facility on drug charges – had been savagely beaten for being a “rat” in a jailhouse hit. The brutal beating left him with a broken leg and finger.

Cameron, 34, who’s doing a nearly 10-year stretch for dealing crystal meth and smuggling in drugs for himself behind bars, was allegedly targeted after a New York mob­ster offered a paltry $100 bounty on him for being a “snitch” and agreeing to testify against his drug suppliers.

The former DJ pulled out of fall flag-football games between inmates after hearing about the threat, says the source, but he still turned up at the prison sick bay a short while later looking like he’d been run over by a truck! He told the prison medical staff that he’d been injured playing handball, but no one is buying that story.

His thighbone was so badly broken he needed a rod inserted and was still on crutches two months after the incident, the source revealed.

“Michael can’t help worrying about what will happen next time,” said the source. “He now goes to bed every night worrying if he is going to get that dreaded phone call that his son was beaten to death in prison.”

At a 2010 bail hearing, Cameron’s psychiatrist let it slip that he was prepared to testify in court against his suppliers, Mexican brothers David and Eduardo Escalera.

Since then, dad Michael, 68, has begged him to “keep a low profile,” but the source says Cameron has “gone gangsta” behind bars, buffing up in the gym and spending more than $1,000 on prison tattoos.

“Michael’s big fear is that Cameron is going to find himself in more trouble than he can handle,” added the source. “For all his wealth and fame, there’s nothing he can do to protect Cameron while he’s inside.”

Michael’s been attending appeals hearings In manhattan to see if  a judge might reduce Came’s sentence – no luck, so far.