The authors report small-angle neutron scattering measurements of pre-percolation clusters in Cu-16.7 at.% Mn at temperatures between 5 and 220K. They draw on the results of Monte Carlo computer experiments which show that pre-percolation clusters are diffuse and ramified, and fit their data by analogy with light scattering from Gaussian polymer chains. The average radius of gyration of a cluster at low temperatures is about 26 AA. By considering the topology of random lattice animals, they estimate that the average cluster contains about 170 Mn atoms.