The transformation sequence of melt-spun Al-5.2at.% Ni-6.8at.% Yb is characterized by X-ray diffraction, differential scanning calorimetry (DSC), and atom-probe field-ion microscopy. An isochronal DSC thermogram detects three major exothermic transformation steps, with onset temperatures of 180, 292, and 327 o C, respectively. Atom-probe analyses reveal the evolution of compositional inhomogeneities on an atomic scale. In addition to Ni-clusters present in the as-quenched alloy, Ni-Yb co-clusters form during isochronal heating to 188 o C. Al-rich precipitates are detected after heating to 250 o C, with the Ni and Ni-Yb clusters still present, constituting possible precursors of intermetallic phases formed during advanced transformation stages.