The Netherlands star felt that they should have defended more solidly against Arsenal’s corners.
The Gunners scored twice from two set piece situations to get a 2-0 win at home on Wednesday.
"In the defensive phase, the amount of chances we conceded without the set plays (was good)," he told MUTV.
"In the end, we played a little bit more offensive and conceded some chances at the end.
"But in general, we have to - and we will - offensively improve. We need to know what everyone is doing and we could have hurt them much more. We're still quite early with the new coach but there are still positives. But overall, I'm really disappointed with the lack of points.
"As you mentioned, we're on the road to improve as a team and I think the manager said it also: maybe if we do it a certain way we have a bigger chance of getting results right now.
"But in the future, we will stay the same and won't improve. I think the way we are going now is obviously not perfect yet and everybody has to improve a lot and get used to the new system, but you can see certain things that are improving.
"But in the end, we are Manchester United and it's easy - it's not good enough. We know that, we will work hard, we have to improve and we have an important game in a few days."
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