Rooney admits it has been a concern inside the United dressing room.
"I can't put my finger on why we are not killing teams off," said Rooney. "We have scored plenty of goals. It is the most number we have scored at this stage of the season.
"We have conceded too many and have done throughout the season.
"But that is the way we have been set up to play. We have to just keep our scoring going."