GoKawiilA tight little cluster hidden in the 2025-26 Champions League draw shows why the “new format” needs one small tweak, and gives a beautiful excuse to talk about symmetric graphs.
TL;DR: UEFA’s new league-phase format can accidentally produce small clusters of teams that play each other disproportionately often, hurting their collective chance of advancing all at once. A single symmetric graph on 36 vertices, C(36; ±{1, 4, 10, 17}), eliminates this risk provably. Deploying it needs one small tweak to the country rule for UCL/UEL, and no tweak at all for UECL.
Napoli, Benfica, Chelsea, Ajax, Qarabağ.
In the 2025-26 UEFA Champions League, they are scheduled to play each other in nine of the ten possible pairings. Only Napoli-Ajax is missing from a complete round-robin among the five. The other nine (Napoli-Benfica, Benfica-Chelsea, Chelsea-Ajax, Ajax-Qarabağ, and five more) all happen in the league phase.
UCL 2025-26 - 9 of 10 possible games scheduled.
That’s an oddly tight little cluster in a 36-team competition. And it’s the kind of thing that isn’t supposed to happen anymore.
Except it does, every season, in almost every UEFA continental competition. In UCL 2024-25 (the first year of the new format), Bayer Leverkusen, Atlético Madrid, Feyenoord, RB Salzburg and Sparta Prague play each other 9 of 10 times. In UEL 2024-25, Roma, Tottenham, AZ, Galatasaray, and IF Elfsborg do the same. UEL 2025-26 has a maximum 5-team cluster of 8 out of 10; UECL 2025-26 has 7 out of 10.
UCL 2024-25 — 9 of 10 UEL 2024-25 — 9 of 10 UEL 2025-26 — 8 of 10 UECL 2025-26 — 7 of 10
Click to expand: full stats across all five competitions **How many dense clusters, per season?** Season 5-team clusters with ≥7 matches ≥8 matches =9 matches 4-team clusters with ≥5 matches =6 matches UCL 2024-25 225 17 3 84 4 UCL 2025-26 332 29 1 109 5 UEL 2024-25 240 17 2 87 3 UEL 2025-26 146 6 0 60 0 UECL 2025-26 (6 matches, not 8) 35 0 0 14 0 Two things jump out: (i) every completed UCL/UEL season has produced a cluster with 8 or more internal matches, and (ii) 2025-26 UCL is actually the season with the most 8+ clusters we have on record (29 subsets), though only one hits 9. UECL is meaningfully less dense because it uses a sparser structure (6 opponents per team, not 8).
What UEFA changed in 2024
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