Rooney, 28, was handed the armband at United when Dutchman Van Gaal took the reins in the close-season, however the club's fortunes have not changed dramatically after their flop under David Moyes.
Moyes led United to a seventh-placed finish in 2013-14, sacked before he served his first season out, while Van Gaal has managed just one win in five league matches plus a dispiriting 4-0 League Cup defeat to third-tier MK Dons.
The former Netherlands boss said Rooney was not up to standard, despite scoring two goals so far, and said Radamel Falcao was more likely to lead the line in future.
"We have played well, but can improve, and I was not so satisfied with Rooney as a striker and [Juan] Mata as midfielder," Van Gaal said.
"That is why I changed. Rooney can play in more positions, he's a multi-functional player and I have tried him in a striker's position.
"He has played well, but not spectacular. Falcao is a striker and I think he can do it better."
England international Rooney also conceded his days as a hit-man are numbered.
"I'm not the player I was," Rooney said.
"But I feel I have progressed my game. I agree with the people who say my game has changed.
"I did too much running when I was younger and then didn’t have the energy to get myself into goal-scoring positions in the box.
"I'm a cleverer [sic] player now and know when to run into the box and when not to, and as a result more chances have come my way and I've scored a lot more goals for the club.
"But I am happy to play out wide. I can do a job there and I can do a job up front. It depends on the situation of each game and what the manager wants me to do.
"I don't think anyone can put a finger on my best position, but I am adaptable. I can go into midfield, drop out wide or play up-front. It just depends on where the manager wants me to play."
