Quantum spin liquids are a novel state of matter predicted to arise in quantum antiferromagnets where geometric frustration and quantum fluctuations are strong enough to prevent a magnetically ordered ground state. At half filling, fractional spin-carrying excitations termed spinons dominate the low-energy physics. Here we present scanning tunneling microscopy studies of the behavior of magnetic adatoms deposited onto the quantum spin liquid candidate single-layer 1T-TaSe₂. Spectroscopic imaging of pristine single-layer 1T-TaSe₂ reveals long-wavelength density modulations at the Hubbard band energies consistent with a spinon Fermi surface instability as predicted by theory. Magnetic atoms deposited onto the 1T-TaSe₂ surface bind at different sites in the star-of-David unit cell and exhibit distinct spectroscopic features near the Hubbard band edges. One possible explanation for the observed behavior is exchange coupling between magnetic adatoms and itinerant spinons.