Ahead of that game, Onana was described as one of the worst goalkeepers in United's history by former United midfielder Nemanja Matic, and the stopper subsequently had a night to forget in France.
He was then dropped for Sunday's Premier League loss against Newcastle, garnering plenty of scrutiny from media and fans, but Amorim confirmed on Wednesday that Onana will be reinstated in goal for the second leg at Old Trafford this week.
"You try your best to ignore it all. Focus on your job, come in on a daily basis and do your best," Maguire said when asked about Onana.
"I always said to myself, 'that's all you can do'. Tomorrow night is another game of football, and you go on that pitch and you give absolutely everything.
"When you walk off you say to yourself 'I have left everything out there', and no matter how you perform that is only what you can do.
"It is the same for any player who wears this badge, it comes with a responsibility to perform. When you don't perform and when the league results aren't good enough, there are people who come under the spotlight.
"I have been in that situation myself, but all you can do is day-in day-out, do your best, work as hard as possible and take each game as it comes."
'We've been far too inconsistent'
Sitting in 14th place with only 38 points after 32 games in the Premier League, United are set to complete their worst ever season in the English top flight.
"It's been a disappointing season. There is no doubt about it. From the start of the season, we have been far too inconsistent," Maguire said.
"I think the performances have picked up of late. However, I still think there are key aspects in the game where us players have got to take more responsibility and have to change them in our favour.
"There have been a lot of games that have been 50/50 and we have ended up on the bad end of a result. That is something we need to work on as a team, as a group of players.
"Tomorrow night is an important night for us in the competition. A big game at Old Trafford, European night and one we are looking forward to."
The England international said even if they win the Europa League, it would still not be considered a good season, but says it would be a "big bonus" to qualify for the Champions League next season.
"It is so important," he said of the trophy. "There is no doubt about it that if we do win the Europa League, it is still going to be a disappointing season for us as players, but winning that would be a big bonus.
"Playing for this club demands trophies, and winning the Europa League would be a special one.
"It would give us access to the Champions League next season, something we obviously cannot gain through the Premier League because our results haven't been good enough."
