We study the electronic structure of the impurity d levels of interstitial Mni in a GaAs quantum well. Unlike bulk GaAs, where the position of the donor states is known to be within the conduction band, we found that in a quantum well, the donor states are bound and located within the band gap. The position of the d levels is determined by the sum of the Hilbert transforms of the density of states. Here we deal with a partial density of states projected from the total density of states by the hybridization matrix elements. Lowering the symmetry of the band states in 2DEG lifts symmetry bans on the hybridization matrix elements. Thus, the hybridization of the d levels with the states near the bottom of the quantum well subband becomes nonzero, which changes the structure of the impurity states compared with those of the bulk GaAs case. Dimension lowering results in quenching of the impurity level splitting originally caused by the crystal field interaction.