New coach Erik ten Hag watched on as Manchester United lost 1-0 away to Crystal Palace on Sunday.
The result saw them secure a ticket to next season's Europa League after they ended their Premier League campaign in sixth place.
Forward Wilfried Zaha scored against his former team in the first half as Palace celebrated their first-ever Premier League victory over United at home.
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Ralf Rangnick's tenure as interim manager came to an end with United collecting 58 points, their lowest tally in Premier League history.
United were nevertheless able to hold on to sixth place after West Ham United suffered a 3-1 defeat at Brighton & Hove Albion and had to settle for seventh.
"The level we have shown in the last three or four months isn't enough to win a Premier League match. We were sloppy, we lost some easy balls around our box, it's impossible to win the games," United goalkeeper David de Gea told MUTV.
"I just want to be positive, to forget about this season."
Watched by new manager Erik ten Hag from the stands, United produced a lacklustre display and went behind in the 37th minute as Zaha finished smartly from the edge of the box after picking up a loose pass and cutting across the United defence.
The visitors tried to improve their game in the second half but they looked poor in attack and barely created chances as Patrick Vieira's Palace ended the season on a winning note and took the 12th spot.
"The new manager was in the stands, so that's a good signal. I hope things will get better for next season -- that's the past already," De Gea added.
"We all know it's been a bad season, for everyone."