Published on: December 2, 2010

NEW DETAILS: JUSTIN TIMBERLAKE was doing his own stunt when filming a scene from his sci-fi thriller when something went horribly wrong!  And now production has been shut down for a week, a source told The ENQUIRER exclusively.

Justin jumped over a railing, twisted and landed on a marble floor.

The crew gasped as they heard a loud crack!

Justin popped something in his knee, according to a source. 

While Justin was in obvious pain, he chose not to go to the hospital but instead had his own physical therapist already present on set who attended to his injury.

According to a production insider, Justin pulled his calf  muscle,  affecting the left side of his knee and how much weight he could put on that leg

In between takes, Timberlake was seen hobbling around on crutches. 

But when director Andrew Nichols called "Action' the gamey actor was all business -- especially with costar Amanda Seyfried

Ironically, the title of the film has now been changed from I'm Mortal to simply Now.

-- RICK EGUSQUIZA in Los Angeles
    special to NationalEnquirer.com 

update: 12/3/10 440 EST
first posted:  12/2/10 430 PM EST