
The midfielder missed Villa’s 1-0 defeat at Fulham on Saturday afternoon, where Ryan Sessegnon scored the only goal of the game late in the first half.
Lamare Bogarde started in place of Onana, whose run of nine consecutive Premier League starts came to an end this weekend.
After the match, Emery provided an update on Onana’s fitness when asked whether the Belgian would be available for the Europa League semi-final first leg.
"I don’t know if he will be available for Thursday,” Emery said. “It's about how every day he is progressing.
“I don't know if he will be ready for tomorrow, Thursday or next Sunday. The only player we know can't play is Barkley as he is not in the list."
Before kick-off, Emery explained: "He was not feeling good yesterday. He had some small pain."
Villa will also be without winger Alysson on Thursday as he was not included in the European squad for the knockout stages.
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