Boss Unai Emery was forced to omit one senior player from the club’s list due to Uefa rules around “club-trained” players.
Barkley, yet to make an appearance for Villa this season, is the man who has made way.
The 31-year-old, who joined the club from Luton for £5million last year, has been struggling with fitness issues through pre-season.
Clubs are allowed to name up to 25 players in their A-list squad for the Europa League but four of those must qualify as “club-trained” - meaning they have been registered for three full seasons, or 36 months, between the ages of 15 and 21.
The deadline day signings of Victor Lindelof, Jadon Sancho and Harvey Elliott left Villa with 22 non club-trained players, meaning one would have to be left out.
It is not the first time Emery has been forced into a difficult decision by Uefa’s rules, with the boss also leaving January signings Andres Garcia and Donyell Malen out of last season’s Champions League squad, due to limits on how many new players can be registered for the knockout rounds.
Both Garcia and Malen have been included in the Europa League squad. Academy product Lamare Bogarde, now a regular part of Villa’s first-team set-up, is on the B-list of players as he qualifies as homegrown.
Barkley scored four goals in 29 appearances for Villa last season but missed a large chunk of the second half of the campaign due to a knee injury.
Emery was hopeful of seeing “the best” of the former England international this term but injuries have again disrupted his progress.
Villa begin their Europa League campaign at home to Bologna on September 25, before their first away match of the tournament at Feyenoord on September 2.