Single Ni, Co, and Cu atoms deposited in the center of cobalt nanoislands grown on Cu(111) are investigated b low-temperature scanning tunneling spectroscopy. The surface states of this model magnetic nanolead are unveiled and assigned to arise from atomiclike and surface-induced states by ab initio calculations. Contrary to the first, the second contribution is predicted by calculations to favor a change in sign of the spin polarization with respect to the pristine lead.