Wayne Rooney acknowledges Manchester United's hopes of finishing in the Premier League's top four are slim after a 2-1 defeat at Sunderland on Saturday.

MATCH REPORT: Sunderland v Manchester United

Louis van Gaal's side was second best for much of the encounter and paid the price when David de Gea conceded an unfortunate own goal in the closing stages after Anthony Martial had canceled out Wahbi Khazri's opener.

United's tally of 41 points is its worst after 26 matches in Premier League history and the club sits six points adrift of the UEFA Champions League places — a gap that could increase further when Manchester City faces Tottenham Hotspur on Monday (AEDT).

After United's first league defeat at Stadium Of Light, Rooney has suggested that winning the Europa League could now be his side's best hope of qualifying for Europe's top competition next season.

"We didn't create enough chances, we were not aggressive enough and didn't defend set-pieces — it is a disappointing result," the 30-year-old striker said.

"We didn't play well. We know that we didn't win enough second balls. It has cost us and it is not good enough. We have to somehow move on. You don't know how this league works at times, but we know it will be hard to finish top four now. 

"Winning the [UEFA] Europa League gets you into the Champions League, but that is a long way away. It is a competition we didn't want to be in, but we are in it now and want to win it. We have to try and start again on Thursday."

United travels to Denmark to face FC Midtjylland in the first leg of its UEFA Europa League last-32 clash on Friday (AEDT).