EE AND A LOADER OPERATOR WERE REPLACING A GUARD ON THE PRIMARY THAT HAD BEEN REMOVED FOR MAINTENANCE. WEIGHING APPROX 150 LBS THE GUARD WAS BEING LIFTED BY A CHAIN ATTACHED TO A LOADER BUCKET. THE CHAIN HOOK WAS USED TO ATTACH THE GUARD. THEGUARD SLIPPED FROM THE HOOK, FELL TWO FT AND STRUCK EE'S FOOT.