The 39-year-old actor spent a week shooting a scene in which his character tumbles down stone steps while high on Quaaludes and is now suffering severe back pain, reported Showbizspy.
"He says he is in nonstop pain and has gained weight because he can't exercise," a source said.
"It hurts to lie down for too long, and it is agony to twist his body into any crazy positions. He considers it the role of a lifetime. Of course, it would ease the pain if he won an Oscar," the source added.