The fourth sub rule would be available in knockout-stage games and will also be applied by FIFA at this year’s World Cup in Russia, having previously been used for the 2016 Rio Olympics.
UEFA has also changed the rules regarding cup-tied players, with January signings set to be able to play for their new clubs in European competitions even if they have already featured for another team.
For example, Barcelona’s Philippe Coutinho has been unable to play in this year’s Champions League knockout stage after joining from Liverpool in January, but under the new rules, players in the same situation next season will not be cup-tied.
UEFA said that each team can add three new players to their squads for the knockout rounds “without any restrictions”.
Teams in the Champions League, Europa League and Super Cup finals will also be able to name 12 substitutes instead of seven.
The kick-off times for the Champions League have been changed from the traditional 1945 GMT slot to 2000 GMT, with group-stage matchdays to have two games played at 1755 GMT in an apparent attempt to maximise income from television rights.
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