Villa, pre-season favourites to win Europe’s second-tier competition, trail 1-0 after last week’s first leg of the all-English clash.
The Birmingham club reached the Uefa Conference League semi-finals in the 2023/2024 campaign and the last eight of the Champions League last season.
Villa are on course to qualify for next season’s Champions League but have stumbled in recent weeks, losing their past three games in all competitions.
Emery, who has won the Europa League four times in his managerial career, with Sevilla and Villarreal, said the result of Thursday’s second leg at Villa Park would not define the club’s season.
“We are improving, myself as well, improving here,” the Spaniard told reporters on Wednesday.
“And we will have, after tomorrow, our way to set more challenges for the present or future.
“I don’t think tomorrow is the last opportunity for us or for anyone. And the players, of course, they are enjoying the process we are doing, and they are aware about how difficult is football, but how the greatest moment we are having here in Aston Villa the last three years, and we can smile and we can be proud of everything,” he said.
Emery said reaching the semi-finals was a “huge achievement” as he seeks to end Villa’s 30-year wait for a major trophy.
“Winning a trophy is very difficult,” he added. “Very, very, very difficult. It’s not a defeat if we are not achieving a trophy.
“The only way forward is to keep going, improving, having opportunities in the present and the future. We now have the opportunity, but only one team wins.
“When I spoke before the first leg, we had 25% of the possibility to win a trophy. Now it’s maybe less because we started losing,” he said.
The match pits two clubs rich in European history against each other – Forest were continental champions in 1979 and 1980, while Villa claimed the crown in 1982.
Emery said Forest, unbeaten in 10 games in all competitions, were favourites, but he was relishing a “fantastic” end to the season after a poor start.
“I am excited, 100%. So, so motivated. When I arrived here three and a half years ago, it was a dream to be playing a semi-final in the Europa League.
“And at the beginning of the season, when we were after five matches playing in the Premier League, before we started playing the Europa League, I was worried about how we were finishing the season this year.
“And finishing the season this year like we are now, in the league and in the semi-final, playing the second leg at home here, against Nottingham, is really something fantastic,” he added.