UEFA has introduced some new rules and timings for this season's competition.
From 2018/19, a fourth substitute will be able to be used in extra-time of knockout games, and will not affect the usual three substitutions.
Only for the finals of the UEFA Champions League, UEFA Europa League and UEFA Super Cup, 23 players (instead of the usual 18) will be allowed in the matchday squad, giving coaches the choice of 12 substitutes instead of the usual seven for those showpiece games.
New UEFA Champions League kick-offs
All UEFA Champions League games from the play-offs right through to the final will start at 21:00CEST. However, during each round, two Tuesday games and two Wednesday matches will start at 18:55CEST. All games on the final matchday of the group stage will kick off simultaneously. UEFA could make exceptions to this rule.
As for players' eligibility after the UEFA Champions League and UEFA Europa League group stages, clubs can add three new players without any restriction. This brings the European competitions into line with national leagues, who impose no restrictions on players signed during the winter transfer window.