A coupling assembly including an endpiece defining a fluid flow passageway and being adapted to be secured to an outlet of a fluid-flow circuit, and a coupling member including a body defining at least one housing for receiving locking balls, a slider defining an axial wall of the at least one housing, a control member surrounding the body and slider and being provided with a ball-locking element that is movable between a rest position in which it and the slider, in an advanced position thereof, retain the locking balls in an innermost locking position, and a release position wherein the slider is movable to allow the locking balls to move both linearly and outwardly to an unlocked position thereof, and return elements for returning the control member to its rest position.