United's defeat to Stoke City last weekend was their eighth of the Premier League campaign under David Moyes, and left them seventh in the table, 15 points behind leaders Arsenal.
The defending champions only lost five league games in the whole of last season and Rooney confessed that it has been tough to get to grips with the new campaign.
The 28-year-old even went as far as to suggest that the title could be beyond United this term, but the quest for the Champions League remains a priority.
"We need to do better as a team," Rooney told BBC Sport. "We're not in the best position but will keep fighting and keep going to get ourselves in as good a position as we can.
"We know it's going to be extremely difficult to win the title, realistically top four has got to be our aim. Although we always want to win the league title, maybe it's a bit too far.
"David Moyes is a fantastic manager, I worked with him at Everton and for a number of months at United. He's done everything he can but it's the players that have to do better and hopefully we can do that."
There has been speculation about Rooney's future at Old Trafford, with his contract due to expire at the end of next season, but he is not letting the reports affect his focus.
"I've said all along I'm focussing on my football," he added. "(I) will try to do as well as I can for the team and help the team be successful."
