The disordered ground-state properties of a double-layer quantum antiferromagnet are investigated in the bond operator representation. The intralayer and interlayer couplings are J and J_{perpendicular to}, respectively. In a mean-field approximation, we obtain a spin gap which decreases with increasing ratio lambda =J/J_{perpendicular to} and disappears at the value lambda _c=0.292. In the region 0<or= lambda <or= lambda _c, we calculate the disordered ground-state energy, the intralayer and interlayer nearest-neighbour singlet strengths, and the correlation length.