A plug for closing a neck of a container comprises an obturation cap, which is laid out across an inner aperture of the neck of the container and which is crossed by a driving-in member notably when the container is installed on a dispenser, and a skirt for attachment to the neck, centered on an axis. The cap defines a central cavity for receiving the driving-in member, the bottom region of which is delimited by a breakable part, which is adapted to be set in abutment by the driving-in member until it breaks and which includes a central bottom wall and a side wall provided with breaking lines extending radially to the axis, while the remainder of the cavity is delimited by a tubular part of the cap, which guides the driving-in member.