The neutral matter distribution from the interstellar medium (ISM) located in the vicinity of the galactic Wolf-Rayet (WR) star HD 50896 has been examined by means of HI 21-cm line observations obtained with both low [half-power beamwidth (HPBW)~=34 arcmin] and intermediate (HPBW~=9 arcmin) angular resolution. The most interesting discovery is a huge ovoidal HI minimum spanning the velocity range +1.5 to +10.0 km s^-1, created, very likely, by the joint action of the progenitor of HD 50896 and the WR itself. Inside this cavity, two minima are clearly discernible. The WR star is offset with respect to either the geometrical centre of the main HI void or the inner HI minima. A physical link between S308, the ring nebula associated with HD 50896, and one of the HI minima is suggested by our data. A kinematical distance of ~1 kpc for HD 50896 is derived based on the radial velocity of the HI cavity. The dual HI minimum geometry observed inside the main HI cavity, a feature also seen in the HI distribution of the ISM located close to other galactic WR stars, may be a consequence of the interaction process itself. The ovoidal shape of the main cavity cannot be explained within the framework of the standard interstellar bubble theory. Elongated bubbles may result when the large-scale galactic magnetic field is taken into account.