An aerodynamically constructed covering part for the underside of a motor vehicle, particularly a passenger car, is provided with an inflow opening and an air guiding element arranged adjacent to the inflow opening. In the driving operation, a partial flow of the cooling air flowing through between the covering part and the roadway is guided through the inflow opening and the air guiding element situated at least in areas above the covering part to an assembly and/or a chassis part situated above. In order to simplify the fastening between the covering part and the air guiding element, it is provided that the air guiding element is inserted into a receiving opening of the covering part and is separably connected with the covering part by way of slide-detent connections.