We plan to investigate by means of zero-field muSR the doping dependence of the sublatticemagnetization in La2Cu1-xZnxO4 and in La2Cu1-xMgxO4. In both systems Cu2+ S=1/2 spins are replaced by S=0 impurities and to a first extent the effect of both substitutions should be the same. However, new exchange paths involving the impurity atomic orbitals can arise and induce afrustration of the Cu2+ S=1/2 square lattice. Accordingly an impurity-dependent decrease of the sublattice magnetization should be observed and the x-dependence of the local field at the muon, at low T, should be different for Mg and for Zn-doped La2CuO4.