Tom Selleck Secret Medical Crisis: Riddled With Unbearable Pain, Forced to Use Stunt Double on 'Blue Bloods'

Famed actor Tom Selleck has been battling a secret medical crisis and is riddled with pain so severe he was forced to use a stunt double on crime drama Blue Bloods, RadarOnline.com has learned.

Sources close to Selleck, 78, said he's been putting on a brave face and still showing up to work despite the constant torment of arthritis. "Tom's in a lot of pain and agony," a tipster said, praising him for "gutting it out, but it's obviously affecting him."

"He's been to doctors and has learned techniques to alleviate the pain, but it's a disease that isn't going to go away," the source said. "He's learning to adjust to it as best as he can."

Selleck's rep, meanwhile, insisted he is "fit and vigorous," denying that he is in "constant pain."

Insiders believe Selleck is just being a trouper, adding that traveling from his 65-acre avocado ranch in Ventura County to TV locations in New York City has taken its toll on the star. Those in his inner circle said he'd prefer to be spending more time with his wife Jillie and daughter Hannah.

Sources claimed that due to Selleck's body allegedly slowing down, the show employed a stunt double to film ordinary scenes.

The actor sometimes has to film his sitting down and often gets winded from the exertion. However, the insiders admit he can't be expected to perform the same stunts he did 35 years ago during eight seasons on Magnum, PI.

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"Tom's days as the car-jumping, scuba-diving action star are a thing of the past," they explained. "Like most stars, there's a stunt double for dangerous action shots, but Tom even uses the guy for simple scenes, like getting out of his police car. His arthritis bothers him more some days than others."

Even though it's been a tall order, Selleck was commended for being an "old-school, true professional" who never complains and gets the job done.