Abstract: A walking aid for a four-legged animal having disabled hind legs comprises an engagement member for engaging a body portion between fore legs and hind legs of the animal; a collapsible resting mechanism connected to the engagement member and to at least one wheel assembly in contact with an underlying surface; and a locking mechanism operatively connectable to the at least one wheel assembly in such a way that the at least one wheel assembly is freely rotatable during forward motion of said walking aid but is rotationally immobilizable following rearward motion of the walking aid. The resting mechanism is operational to facilitate movement from a walking state to a resting state or from a resting state to a walking state only when the at least one wheel assembly is rotationally immobilized.