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A 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 For decades, the Champions League and its sister competitions used the same shape: 32 teams, 8 groups of 4, a round-robin within each group. Each team played 6 group-stage matches (three opponents faced twice each) before the top two per group advanced. In 2024-25, UEFA scrapped that. In its place: a single 36-team “league phase” where each team plays 8 different opponents (2 from each of 4 seeded pots), and a single 36-team table sorts everyone into three buckets: top 8 auto-advance to the round of 16, teams ranked 9-24 go to a knockout playoff, teams 25-36 are eliminated. The same format runs across all three UEFA men’s competitions: Champions League (UCL), Europa League (UEL), Conference League (UECL). The sales pitch was reasonable. More marquee matches. More competitive standings. No more “dead rubber” final matchday when both advancing teams have qualified already. And the “single table” framing removes the arbitrary group draw, which had famously produced imbalanced “groups of death” for years. But it introduced a subtler risk that nobody flagged at the time. Here’s the thing about 36 teams each playing 8 opponents: it produces a huge network of 144 matches, and inside that network you can find small clusters of teams that happen to play each other disproportionately often. Not because anyone designed it that way; because the draw is random and 144 edges among 36 teams have to land somewhere. Think of the league phase as a graph: 36 nodes, one per team; 144 edges, one per scheduled match. Every team-node touches exactly 8 edges (its 8 opponents). A dense cluster is a small clump of nodes with an unusually large number of edges inside the clump.
Here’s what the actual 2025-26 UCL looks like as one such graph: UCL 2025-26 as a graph. 36 team-nodes around the ring, grouped by pot; 144 match-edges drawn as chords. The 9 red edges are the internal pairings of the Napoli-Benfica-Chelsea-Ajax-Qarabağ cluster. Want to poke at the graph yourself? Here’s an interactive viewer for all five past draws (UCL, UEL, UECL, 2024–26) with re-layout, pot/country coloring, and cluster highlighting. The Napoli-Benfica-Chelsea-Ajax-Qarabağ cluster is the extreme case. Of the 376,992 different ways to pick 5 teams out of 36, the actual UCL 25-26 draw has 332 different 5-team clusters with 7 or more internal matches, 29 with 8 or more, and exactly one (the Qarabağ cluster) with 9, the unique maximum. Why does that matter?