Thanks to his World Cup commitments with Netherlands, the Dutchman only oversaw his first Red Devils training session on Thursday before flying out to the United States for the club's pre-season tour but has been impressed with the players so far.
"I have to say that it has been fantastic," Van Gaal told reporters at the Rose Bowl Stadium ahead of United's first pre-season fixture against LA Galaxy on Wednesday.
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"The focus I have seen in the training sessions is top-level but we have to see if the performance is top-level but I am very happy with the labour of my players in the days I have been with them."
United's trip to USA, which will also pit them against Roma, Inter and Real Madrid, is a chance for Van Gaal to assess his playing stocks before adding to the signings of Ander Herrera and Luke Shaw. The manager wants to give all his players a chance to prove themselves, including striker Javier Hernandez, who was out of favour last season and has been linked with a move away as a result.
"I have to see if he performs how I want," said Van Gaal of the Mexican. "Now I can only see what he has showed under the guidance of another coach.
"He will arrive [on Tuesday] evening and I will meet him, we will train and after that he will perform in a match and then I can say something about that."
Van Gaal also refused to comment on transfer targets, with Juventus star Arturo Vidal understood to be at the top of his wishlist.
"I want to learn about my players, to know them and, when I give the orders, I want to see how they perform," he added. "That is why I cannot answer this question now. I want to give all the players a chance to show themselves under my guidance."