The same applies to the Europa League. Under current rules, clubs who qualify for the knockout stage of either the Champions League or Europa League are allowed to register three new players. These can include one player who has represented a different club in the Europa League group stages but none who have been fielded for another club in the Champions League group stage. The present ruling prevents Barcelona from fielding Philippe Coutinho in the Champions League this season as he has already played for Liverpool.
Uefa's rules have been changed.From next season, players will be able to represent two different clubs in the same European cup competition.https://t.co/qmymQjn3dU pic.twitter.com/7DXl5sb4iG — BBC Sport (@BBCSport) March 27, 2018
Alexis Sanchez was eligible for Manchester United, however, as he switched from Arsenal in the Europa League to the Champions League. The new rules state that "that a club may register three new eligible players without any restrictions." Uefa said the new ruling brought it into line with domestic leagues which "do not impose restrictions on the eligibility for competitions of players registered for a new club during the winter transfer window." Uefa said the fourth substitution will be allowed following its approval by soccer's law-making body IFAB on March 3. It said that 23 players, instead of 18, would be allowed on team sheets for the Champions League and Europa League finals, and the European Super Cup match.
All eyes on the January transfer window ?Uefa has announced rule changes for next season's Champions League and Europa League. ? https://t.co/qmymQjn3dU pic.twitter.com/B41PcNq3je — BBC Sport (@BBCSport) March 27, 2018