Melee icon missing
 

I am playing the single player mission Chasing Shadows and melee is disabled. At first I thought it was a glitch, so i was messing around with the icon and hot keys. I accidentally dragged the icon from the hot bar and attempted to place it in the attack options to the bottom right of the screen. After I let go of the icon it disappeared, not placing itself in the square i tried to put it in. So it is now neither in the hotbar or the attack options, crouching, etc thing to the bottom right of screen. I have looked everywhere for this icon so i can place it back into the hotbar. Where is it!! Please Help! I have tried reloading a previous save to fix it but it didn't work.

Also, while looking for help on the internet, i noticed that it is disabled for everyone and it is not a glitch. D: