[en] A dechanneling treatment, previously developed for perfect crystals and for those covered with amorphous layers,is extended to the case of a damaged crystal. The minimum yield and the angular yield profiles have been measured in Si damaged by 0.3 MeV deuterons as a function of penetration depth by backscattering of MeV deuterons. In the case considered, i.e., low defect concentration, the aligned yield at a given depth results from wide-angle scattering on defects lying at the same depth, which adds to the dechanneled fraction. The last depends on the concentration of defects, which being spread inside the crystal contribute to multiple scattering in the channel as electrons and thermal vibrations do. The defect contribution should then be added to the electronic and nuclear reduced multiple scattering. The dechanneled fraction has been obtained in the steady increase approximation as a function of the experimental parameters and of the defect concentration and profile. The comparison of the calculated minimum yield with experiments shows an extremely good agreement. (U.S.)