EE & HIS SUPERVISOR WERE INSTALLING THE 2ND COMPARTMENT DOOR ON FM#2 BALL MILL. EE PICKED UP ONE OF THE DOOR CROSSBARS & FELT SOMETHING PULL IN HIS BACK. HE WORKED THE REST OF HIS SHIFT & NEXT DAY. HE WAS OFF SHIFT FRI-SUN, 8/16-18 & HIS NEXT SCHEDULED SHIFT WOULD'VE BEEN MON 8/19. HE CALLED IN THAT DAY SAYING HIS BACK HURT BAD & HE NEEDED TO SEE A DR. HASN'T RETURNED TO WORK YET.