Louis van Gaal insists the result was not a fair reflection of their performance in their 0-0 Champions League draw with PSV Eindhoven.
United failed to turn dominance of the ball into a victory at Old Trafford on Wednesday night and must now win at Wolfsburg to guarantee progress from Group B.
Van Gaal concurred with Rooney’s assertion that United need to score more goals but does not believe his side have been playing badly.
Asked if he agreed with Rooney’s comments about ruthlessness, Van Gaal said: “Yes, of course, because we are playing football to win – that is what he is saying, and I am saying that always.
“We have to win. But you cannot do it always.
“Of course I am worried (about the scoring rate) but I know also that goals are coming and going – it is not a consequence of good or bad performances.
“Today we could have scored at least three goals. They were not the most difficult chances but we didn’t score. Then, the next game you can score out of nothing – that is football.
Van Gaal is in no doubt the assignment ahead in Germany is trickier than the one they failed to pass against PSV.
“The result is disappointing because I feel we could have finished this game several times,” Van Gaal said.
“In the first half it was average and in the second half in spite of my changes it did not improve.
“Nevertheless, in the second half we gave only one chance away – so then you know at the end it is 0-0. That is disappointing, because we have to win in Wolfsburg.
“We are second so we are in the qualifying position, and we have to do it in Wolfsburg. But it is more difficult. It would have been much easier if we did it tonight.”
He then sounded a note of optimism, as he added: “We have won already our home match against Wolfsburg (2-1 in September), so why can’t we win in Wolfsburg?”
Cocu on Man Utd’s style
PSV coach Phillip Cocu was delighted with his side’s efforts and felt United’s confidence had drained as the contest went on.
Asked whether he thought United’s style was boring, Cocu said: “I think they want to dominate the game.
“That is their style and in the first 20 minutes they showed a lot of power going forward and created some dangerous situations.
“But we felt as the game went on and they couldn’t score a goal, they were not so dominant anymore.
“They couldn’t find a solution of beating our defence. Tactically, we were very good.
“Maybe (in terms of) the confidence, they didn’t believe any more in the last part of the game that they could win it.”