Can a football player play in champions league if he played in Europa league?

Answer 1

In limited circumstances, yes. UEFA regulations state:

18.07 Excluding the UEFA Super Cup, and subject to paragraph 18.18 below, a

player may not play UEFA club competition matches for more than one

competing club in the course of the same season. A substitute player who is

not fielded is entitled to play for another club competing in the same season's

UEFA club competitions, provided that he is registered with the UEFA

administration in accordance with the present regulations.

18.17 For all matches from the start of the round of 16, a club may register a

maximum of three new eligible players for the remaining matches in the

current competition. Such registration must be completed by

1 February 2010 at the latest. This deadline cannot be extended.

18.18 One player from the above quota of three who has played UEFA club

competition matches for another competing club in the current season may

exceptionally be registered, provided that the player has not been fielded:

- in the same competition for another club;

- or for another club that is currently in the same competition.

Furthermore, if the player's new club is playing in the UEFA Europa League,

his former club must not have played in the UEFA Europa League at any

point in the current season

So a player that played in the Europa League can play for another club in the Champions League, but only from the Round of 16, providing he was registered prior to the deadline. Clubs may only register one such player, and if the A list is already full, must remove a player to register another.