The application relates to needle protection assembly (1)) comprising:—a support (2) of the needle (3),—a needle shield (8) having a longitudinal axis A,—urging means (13) for displacing said needle shield (8) from a “in, use” position to a “after use” position,—a locking element (10) intended to prevent said needle shield (8) from moving back from its “after use” position to its “in use” position, characterized in that said locking element (10) has a longitudinal axis B and is radially movable with respect to said needle shield (8) between a “free” position, in which the longitudinal axis A of the needle shield (8) and the longitudinal axis B of the locking element (10) are merged and in which said needle shield (8) is movable from its “in use” position to its “after use” position, and a “locking position”, in which the longitudinal axis B is radially spaced apart from the longitudinal axis A and in which movement of the needle shield (8) from its “after use” position to its “in use” position is prevented.