Dielectric nanoantennas excited at Mie resonances are becoming suitable candidates for nonlinear optical effects due to their large intrinsic nonlinearity and capability to highly confine electromagnetic fields within subwavelength volumes. In this work, we show that a single Ge nanodisk, recently demonstrated as an efficient source of third-harmonic generation (THG), can also be exploited for four-wave mixing (FWM) phenomena. The high field enhancement inside the disk yields effective third-order susceptibilities as high as 2 × 10–8 esu (2.8 × 10–16 m2/V2), which were determined by single pump wavelength THG measurements tuned to high-order Mie modes. A similar nonlinear optical response is observed in the case of degenerate FWM where two different pump wavelengths are coupled to a single high-order resonant mode. However, when the two pump wavelengths are coupled to different high-order modes, the FWM process is partially suppressed due to a diminished near-field spatial overlap of the mixed wavelengths within the disk. This investigation reveals useful pathways for the optimization of third-order optical processes in all-dielectric nanostructures.