EE WAS HELPING OTHER WORKMEN ROLL OVER A PILE OF HIGH VOLTAGE CABLE ON A LONGWALL RECOVERY SECTION. HE STEPPED ON A PIECE OF BELT STRUCTURE THAT WAS LYING ON THE MINE FLOOR & FELT PAIN IN HIS LEFT KNEE. THERE WAS NO DAMAGE OR IMPAIRMENT TO MINING EQUIPMENT OR TO THE OPERATION. EE WAS NOT AWARE THAT THE BELT STRUCTURE WAS IN HIS WALKWAY. NO OTHER FACTORS WERE INVOLVED.