THE EMPLOYEE WAS WALKING DOWN A FLIGHT OF STAIRS WITH A GREASE GUN IN ONE HAND AND AN AIR FILTER AND SMALL OIL CAN IN ANOTHER. AS HE TOOK THE LAST STEP TO THE GROUND HE STEPPED DOWN AND HE SAY S HIS KNEE JUST GAVE OUT, BOWING TO THE OUTSIDE.WHEN HE CAME TO WORK THE FOLLOWING MONDAY, 6-11, THE KNEE WAS SWOLLEN AND PAINFUL TO WALK ON. HEADVISED SUPERVISOR OF INJURY MON.MORNING 6-11.