Guard structure (10) for protecting a lower limb, comprising a number of substantially rigid members (14, 26, 32), which are adapted to be removably and adjustably applied on to the thigh and the calf of the user. These rigid members are connected with each other in such a manner as to allow for the length of the entire structure to be adjusted in accordance with the actual length of the limb, in particular of the calf, while keeping the rigid members themselves joined with each other. The lower end portion of the structure, which is intended for wearing under the usual garment, is anchored in an adjustable manner to a containment shell (52) for a shoe (36).