Fernandes, who has scored 23 goals and contributed 14 assists in an outstanding first full season at Old Trafford, says there remains much room for improvement for Ole Gunnar Solskjaer's team.
Speaking on talkSPORT before United fly out to Spain for Thursday night's first leg, Fernandes spoke of his ambitions at United.
"No, it is never sufficient when you win just one trophy at this club," he said. "You see in the past they won a lot of trophies.
"It is always successful when you win something because if we win something, we have done something good.
"But at the same time, it doesn't matter how many trophies you win, you always have to improve. If we had won four trophies this season, we still have to improve. And if we just win the Europa League, we still have to improve.
"The most important thing for us is understanding it doesn't matter how many trophies we win, we still have to improve."
He added: "Honestly for us, we are improving as a team because we want to win trophies and everything we are in. But at the moment I think we are not at that level this season because we lost a lot of games.
"Honestly, those games were not the kind of games we expect to lose and we lost a lot of points at home. Away, our form is really different [United haven't lost an away league game all season].
"I think we have improved and this season is not finished. We have a lot to do before the end of the season.
"Until the mathematics is impossible, you have to believe. When it is not possible to catch City, I will forget the league."