Van Gaal takes charge of his first competitive match as United boss on Saturday when Swansea come to Old Trafford.
It will also be the first time Rooney has led the team out in his new role as United's full-time captain.
Rooney was announced as the club's skipper on Tuesday night, following the 2-1 win over Valencia.
Rooney also wore the armband in the friendly victory, but he put in a sub-par performance on the night, missing a penalty in the first half.
Van Gaal believes Rooney has the potential to be an excellent United captain, but the Dutchman thinks the striker must not be overawed by the responsibility.
"I said to him (after the Valencia game): 'Maybe it was too much for you as a captain'," Van Gaal told a press conference.
"But I said to him - 'let it fly', because when we were (on tour) in the US, he scored a lot of goals, and made a great amount of assists so I wanted to say that."
Source : PA
Source: PA