EE WAS GETTING OFF OF HIS STOCKPILE TRUCK WHEN HE SLIPPED ON ICY GROUND & HIT HIS LEFT KNEE ON THE FUEL TANK STEP. THIS RESULTED IN A CONTUSION. ORIGINALLY THIS INCIDENT WAS THOUGHT TO BE A FIRST AID ONLY BUT HE HAS BEEN DOWNGRADED TO MEDICAL/RESTRICTED DUTY. 20 DAYS INTO THE RESTRICTION THIS EE WAS LAID OFF.