The reigning champions have lost their last two league games, to Newcastle and Everton, and travel to Villa Park on Sunday to face Aston Villa with Rooney urging his side to improve.
"We all have to step up," he told reporters. "It hasn't been good enough of late and we all have to come forward and show why we were champions last year and do better.
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Despite United's inconsistent form, Rooney has been impressive this season, scoring 10 times already for the Red Devils, but the England international is unconcerned by his own individual displays.
"It's not about me, it's about the team. If the team isn't doing well then my form is not important – we have to do well as a team and roll our sleeves up and really pull ourselves together," he added.
"We haven't won the games or put ourselves in a position where we can win some games.
"The Everton game [a 1-0 home defeat], we probably had the best chances and lost the game – and that is all you look at.
"We have to be realistic now and try to climb up that table and see where are in four, six or eight games' time.
"It's not nice. We are all proud players and it's not nice being there. It hurts. Hopefully there will be a reaction."
Rooney was at a loss to explain United's form this season, which has seen them lose five times already in the Premier League, but says it is important the team returning to winning ways.
"We don't know why it has happened but it has happened and as a group of players we have to do better. We are not playing at our best and we have to start doing it," he continued.
"It's disappointing to be where we are in the league but there are a lot of games left and a lot of points to play for.
"Especially at the moment we have to take each game as it comes and just keep trying to get three points in each game. Whether that is a 1-0 victory, we have to take it and keep trying to climb up the table."