We report a ferromagnetic resonance (FMR) study of a single crystal of Cr₄PtGa₁₇, the first material of a half-Heusler (HH) type with a metallic ferromagnetic breathing pyrochlore structure. The spatial distribution of the magnetic free energy density derived from the FMR data appears to be of a cubic symmetry despite the lower symmetry coordination of magnetic Cr ions. This surprising finding strongly suggests that the Cr₄Ga₁₄ structural unit at the Y site of the HH general XYZ formula forms an octahedrally shaped integral magnetic cluster, likely due to strong exchange interaction between the Cr ions via covalent Cr-Ga-Cr bonds. The presence of magnetic clusters within a regular metallic lattice appears to be a new intriguing characteristics of these novel types of HH compounds whereas Cr₄PtGa₁₇, at the same time, constitutes the rare example of such metallic pyrochlore-type material.