A fourth substitute can be selected in extra-time in the Champions League and Europa League competitions from next season.
UEFA has introduced new rules that also allow 12 substitutes to be selected from in the finals of both competitions, as well as that of the UEFA Super Cup.
The governing body says this is to give “coaches more flexibility regarding substitutes, and facilitate their squad management for the most important fixture of the season”.
It means the squads for finals will rise to 23 players. The squads for all other games will remain at 18 players including seven subs.
A number of managers have spoken of a desire to be able to select from more substitutes in recent years, including Claudio Ranieri during his time as Leicester City manager.
UEFA have also altered kick-off times for the 2018-19 season, with matches beginning at 7pm (5am AEDT) and 8pm (6am AEDT) UK time on Tuesday’s and Wednesdays.
The rules regarding player registration have also been relaxed so January signings can play for their new clubs in the Champions League and Europa League.
UEFA says starting next season clubs “may register three new eligible players without any restrictions.” Current rules mean Barcelona cannot select Philippe Coutinho in the Champions League because he played for Liverpool in this season’s group stage. And Arsenal cannot select Pierre-Emerick Aubameyang in the Europa League because previous club Borussia Dortmund switched to the same competition’s knockout rounds after he played in the Champions League.
UEFA says the change brings its competitions into line with national leagues, which do not limit January signings’ right to play.
Also from next season, clubs reaching competition finals can use a 23-player squad instead of 18.