Van Gaal admitted he doubted his decision to hand the Old Trafford armband to Rooney earlier this week.
But the newly-installed United boss feels sure he has made the right call, based on the way the 28-year-old performed during the club’s successful pre-season training camp in the United States.
“His attitude on the pitch and on the training ground and off the pitch is very important, and I explained that to him,” he said.
“I like him very much and how he trains and performs. I also liked the way he performed with his fellow players.
“I think what I saw on Tuesday it looked like it might have been too much for him to be captain but I told him to let it fly, just to let it fly.
“In the US, he scored a lot of goals and made a great amount of assists and I want to see that Wayne.”
Van Gaal has a lengthy injury list for his first domestic game against Swansea this weekend with striker Robin van Persie and new signing Luke Shaw (hamstring) ruled out.
Jonny Evans, Antonio Valencia and striker Danny Welbeck are doubtful, which means youngster Tyler Blackett is set to be given his debut while Reece James could start at left-wing back.
"We have started more or less in the US and not here," van Gaal said. "Only a few players have trained here since 7 July and on 18 July we went to the US when I was here.
"Before that, my assistants were it and it was a small group. After a World Cup, all of the players are coming in different moments and it is very difficult to train.
"They are at different levels and we have a big staff so we can do that. But we also have to travel, we have also to deal with jet lag and a lot of matches in 14 days.”