Amadou Onana is out for Villa, having failed to recover from the knee injury which forced him off in the first leg.
The midfielder was a doubt for the game, having missed the 1-0 defeat at Fulham, and came off in the second half at the City Ground.
He did not train with the squad on Wednesday and is sidelined at Villa Park on Thursday.
“Obviously not,” said boss Unai Emery, when asked if the former Everton star was available.
Skipper John McGinn is fit, though, having sat out Sunday’s 2-1 defeat by Tottenham.
“He trained normally and if he is not changing something, he is going to be available for tomorrow,” added Emery.
Villa have lost their two previous semi-finals under Emery – the Europa Conference League to Olympiacos two years ago and last season’s FA Cup semi-final to Crystal Palace.
“Only one team wins. When I spoke before the first leg, we have a 25% chance to get a trophy,” said Emery.
“Now, maybe it is less because we started losing. We have a 50% chance, or maybe less, to play the final. This is football and you must respect every competition and respect Europe. You must respect each team.”
