UEFA's Champions League draw creates unfair clusters; a Cayley graph fixes it

The 2025-26 Champions League league phase placed Napoli, Benfica, Chelsea, Ajax and Qarabağ in nine of ten possible pairings, forming a dense five-team cluster that lowers their joint advancement probability. The season also recorded a record 29 internal-match clusters across the UCL, UEL and UECL. A symmetric Cayley graph on 36 vertices (C(36; ±{1, 4, 10, 17})) can eliminate such clusters with only a minor tweak to the country-restriction rule for the Champions and Europa Leagues.